We sought here to investigate the patterns of Staphylococcus aureus carriage in the first year of life, its determinants, and the dynamics of transmission between mothers and infants. A prospective longitudinal cohort study of S. aureus carriage among mothers and their infants was performed, including monthly screenings from pregnancy/birth through the first year of the infant’s life. Medical and lifestyle data were collected.
KEYWORDS: S. aureus, infants, longitudinal
ABSTRACT
We sought here to investigate the patterns of Staphylococcus aureus carriage in the first year of life, its determinants, and the dynamics of transmission between mothers and infants. A prospective longitudinal cohort study of S. aureus carriage among mothers and their infants was performed, including monthly screenings from pregnancy/birth through the first year of the infant’s life. Medical and lifestyle data were collected. Infant S. aureus carriage was detected from rectal and nasal swabs, and maternal carriage was detected from nasal and vaginal swabs. Multivariate analysis and a nonlinear mixed model (NLMIXED) were used to determine the predictors of carriage and S. aureus persistence. Of the 671 women recruited, 130 women carried S. aureus at recruitment (19.3%); they and their 132 infants were included in the study. A total of 93% of the infants acquired S. aureus sometime during the first year of life; 64% of these infants acquired the maternal strain, mostly (66%) during the first month of life. We observed that 70 women (52.50%) and 17 infants (14%) carried S. aureus persistently. Early acquisition of S. aureus carriage was associated with longer duration of initial carriage and was the most significant predictor of S. aureus persistence, while day care center attendance was negatively associated with persistent carriage. Methicillin-resistant S. aureus was carried by two infants for only 1 month each and not by any of the mothers. Early acquisition of S. aureus, mostly from the mother, is thus an important determinant of carriage persistence in infancy.
INTRODUCTION
Asymptomatic carriage of Staphylococcus aureus is common, with approximately 30% nasal carriage reported in the healthy population. Nasal S. aureus carriage has been shown to be an important source of transmission, as well as a significant source of endogenous infection (1, 2).
Risk factors of S. aureus carriage have been studied extensively in the adult population. Adults have been found to carry less S. aureus as they age, whereas children have been found to have a high carriage rate around birth that quickly drops in the first months and then rises again by the second or third year of life (3, 4). The use of hormonal contraception (5), male gender (5–7). diabetes (8), and skin diseases, particularly atopic dermatitis (9), have been positively associated with S. aureus carriage, whereas smoking has been found to be both predictive (4, 8) and protective in different populations (10). Longitudinal studies that reported carriage patterns have found that 20% of adult healthy population are persistent carriers, typically of a single strain, 60% are transient carriers, and 20% are never carriers (11–13). Much less is known about early infancy carriage patterns or predictors of carriage.
In this longitudinal study, we followed a cohort of infants, born to S. aureus carrier mothers, monthly from birth until the age of 1 year, and we observed and report the carriage patterns and carried strains and their determinants during the first year of life.
(Some of the results reported here were presented at the 3rd International Conference on the Pathophysiology of Staphylococci, Tubingen, Germany, September 2016, and at the 18th International Symposium on Staphylococci and Staphylococcal Infections, Copenhagen, Denmark, August 2018.)
MATERIALS AND METHODS
Institutional review board and patient consent.
The study was approved by the Institutional Review Board of the Sheba Medical Center. Written informed consent was obtained from each woman for her and her newborn’s participation in the study, and unwritten approval from the other parent was also received.
Study design, study period, and study population.
In this prospective longitudinal cohort study, pregnant women at ≥34 weeks of gestation, who visited the monitoring unit during screening hours were recruited and screened for nasal and vaginal S. aureus carriage. Only women who were detected to be nasal or vaginal S. aureus carriers were enrolled and monitored. Recruitment took place for 3 h a week between February 2009 and March 2018 at the Sheba Medical Center obstetrics monitoring unit. The Sheba Medical Center is the largest tertiary center in Israel, with approximately 11,000 births per year. Approximately 400 women visit the obstetrics monitoring unit monthly for various reasons, including overdue pregnancies (40+ weeks), breech fetal positioning, low levels of amniotic fluid, babies with outlying measurements, and monitoring of any pregnant woman who came to the emergency room for any reason. Within 48 h of delivery, the mothers were rescreened using vaginal and nasal swabs. Concurrently, newborns were screened with ear, umbilical, nasal, and rectal swabs. Data addressing demographic details (age, number of siblings, pet ownership, and smoking status), medical history, including obstetric history and pregnancy complications, comorbidity, medication and antibiotic use, previous hospitalizations, and breastfeeding status, as well as pregnancy and delivery details, were collected by using a questionnaire and from the electronic medical files. Screening was performed by the attending midwife, obstetrician, or pediatrician at the delivery room or at the nursery.
Monthly follow-up visits from the age of 1 month and until 12 months of age were carried out by a study coordinator at each infant’s home. During these visits, mothers were screened using nasal swabs, and children were screened using nasal and rectal swabs. Data addressing changing nutritional habits and medical events, including health care visits, antibiotic use, vaccination, and hospitalizations, were also collected.
Laboratory methods.
Nasal screening was performed using a cotton-tipped swab placed in Amies transport medium (Copan innovation, Brescia, Italy). Swabs were streaked on CHROMagar S. aureus plates (HiLabs, Rehovot, Israel) within 24 h and incubated for 24 to 48 h at 35°C. Catalase and staphylase testing (Pastorex Staph-Plus; Bio-Rad, Marnes-la-Coquette, France) was performed on suspected colonies to conclusively identify them as S. aureus. A cefoxitin agar disk diffusion test was used to detect methicillin-resistant S. aureus (MRSA) according to the current Clinical and Laboratory Standards Institute protocol.
The genetic relatedness between mother and newborn strains was assessed by pulsed-field gel electrophoresis (PFGE) and spa typing. Maternal strain acquisition by the newborn was defined as the acquisition of an S. aureus strain that was identical (by PFGE or spa typing) to his or her mother’s strain.
PFGE was performed according to the European HARMONY protocol (14). Briefly, DNA digested with SmaI was electrophoresed in 1% agarose gels for 21 h with a ramped pulse time of 5 to 40 s using a CHEF DRII system (Bio-Rad Laboratories), with S. aureus NCTC 8325 as a reference. Genetic identity between strains was defined according to the method of Tenover et al. (15).
At least one strain from each pulsotype, as well as for any strain where the PFGE result was not available, was spa typed. Spa typing was performed by purifying the PCR product (Gene JET PCR DNA purification kit; Fermentas) of the spa gene encoding protein A using the primers 1517R (GCT TTT GCA ATG TCA TTT ACT G) and 1095F (AGA CGA TCC TTC GGT GAG C). PCR products were Sanger sequenced by Hy Laboratories, Ltd. (Rehovot, Israel), using a BigDye Terminator v1.1 cycle sequencing kit (Applied Biosystems, Inc.) on a 3730xl DNA analyzer with DNA sequencing analysis software v.5.4. The sequences were analyzed using a Fortinbras SpaTyper (http://spatyper.fortinbras.us/) and the Ridom Spa Server (16). The genetic relatedness of the strains was evaluated based on spa repeat patterns using the Tree and Network Inference module of Bionumerics Seven.
Carriage patterns and definitions.
Transient carrier mothers were defined as individuals who were colonized with S. aureus in less than 33% of the available screenings. Persistent carrier mothers were defined as mothers who were colonized with S. aureus in at least 67% of the screenings available. Since most of the newborns acquired S. aureus within the first 2 months of life, using these definitions would define many of the infants as persistent carriers, including those who only carried S. aureus for 2 to 3 months but were lost to follow-up before the end of the year. We therefore used a more stringent definition for infant carriage. Persistent carriage in infants was defined as S. aureus carriage detected in at least 67% of the screenings available and also in at least 50% of the screenings from the second half year of life (age 6 to 12 months). Either rectal or nasal carriage was considered child S. aureus carriage.
Statistical analysis.
Descriptive data analysis was performed, and a chi-square test was used to examine the associations between categorical variables (i.e., the mother’s and the child’s carriage patterns). Spearman’s rho was used to calculated the correlation between continuous variables (i.e., the first month of S. aureus acquisition and the duration of infection).
A multivariate logistic model was used to determine the independent predictors of persistent S. aureus carriage in the child. Any variable with a P value of <0.2 in the univariate analysis was included in the multivariate model. Variables assessed in the univariate analysis included sex, gestational age, birth weight, breastfeeding, pets, antibiotics in first year of life, skin infections, attendance at a day care center (DCC), maternal carriage persistence, maternal carriage in first month of life, and infant carriage in the first 2 months.
To determine the predictors for S. aureus carriage each month during the follow-up period, the demographic and clinical factors that independently predict S. aureus carriage in the following month were assessed. These factors included the infant’s carriage status in the preceding month, the maternal carriage status in the preceding month, DCC attendance in the preceding month, antibiotic use in the preceding month, breastfeeding in the preceding month, and age. To account for the multiple measurements per subject in the longitudinal design, a nonlinear mixed model (the NLMIXED procedure) that fits a logit model was applied. Data were analyzed using SAS v9.4.
RESULTS
Study population.
Of over 2,000 women who were approached, approximately 30% agreed to participate and take part in the monthly visits for the full year of follow-up. They were screened and signed an informed consent. Of the 671 women who were recruited, 136 were carriers of S. aureus in the nose or vagina at recruitment and were enrolled and monitored in our study. Of these, 130 women and their 132 newborns completed at least 6 months of follow-up and were included in the final analyses. Of the planned 12 monthly follow-up visits, 121 of the 130 (93.1%) mother-child dyads completed at least 8 visits, and 103 (79.2%) completed at least 10 visits. The 130 mothers included in the final analyses were between 21 and 43 years old and had a mean education level of 16.2 years (Table 1). A total of 6,043 swabs were collected from the mothers and children, and 1,887 S. aureus isolates were detected, 786 from the children and 1,101 from the mothers.
TABLE 1.
Study population characteristics
| Variable | No. | % | Range | Mean (SD) |
|---|---|---|---|---|
| Mother | 130 | |||
| Age (yr) | 21–43 | 34.24 (±4.71) | ||
| Education (yr) | 12–20 | 16.20 (±2.20) | ||
| Cesarean section birth | 33 | 26.83 | ||
| Child | 132 | |||
| Gestational age (days) | 34.57–42.14 | 39.93 (±1.48) | ||
| Birth wt (g) | 2,030–4,396 | 3,310.41 (±496.12) | ||
| DCC attendance | 74 | 56.06 | ||
| Age at entry (mo) | 3−12 | 7.1 (±2.44) | ||
| Breastfeeding | 119 | 90.15 | ||
| Duration (mo) | ||||
| >1 mo | 114 | 86.36 | ||
| >3 mo | 104 | 78.79 | ||
| >6 mo | 75 | 56.82 | ||
| Antimicrobial use | 72 | 54.54 | ||
| Duration (mo) | 1.81 (±1.25) | |||
| Physician visits (within yr) | ||||
| ≥1 visit | 126 | 95.45 | ||
| >2 visits | 100 | 75.76 | ||
| >3 visits | 78 | 59.09 | ||
| >5 visits | 45 | 34.09 | ||
| Hospitalizations | 12 | 9.09 |
The child population was a normal birth cohort and the children’s characteristics are described in detail in Table 1. Approximately half of the children attended day care center (DCC) at some point during their first year of life and, of those, the median age of entry to DCC was 7 months (range, 3 to 12 months). Most of the children were breastfed (n = 119; 90.2%), and most of these (63%) were breastfed for at least 6 months.
Health utilization during the first year of life was relatively high, with approximately half of all children consuming at least one antibiotic regimen, and 75.8% of children visited their primary care physician more than twice during the year for nonroutine vaccination visits (Table 1). The most common reason for antibiotic treatment was upper respiratory tract infection, and the most commonly prescribed antibiotic was moxypen (amoxicillin).
Isolated strains.
Altogether, 119 clones were detected in 1,887 bacterial isolates isolated from the 130 dyads over the course of the year. CC30 was the most commonly carried clonal complex in our sample, based on identification and grouping of spa-typed strains. It was isolated 134 times; nine different strains belonging to CC30 were isolated from the noses of 23 dyads. t3243 (CC22) was the most frequently isolated single strain; it was carried by 10 dyads (Table 2). No clonal complex was found to be carried more commonly by persistent carriers than by transient or noncarriers.
TABLE 2.
Most commonly carried strains
| Clonal complex | No. (%) of dyads carrying this complex | Spa type(s) (no. of dyads carrying each type) |
|---|---|---|
| CC30 | 27 (20.5) | t012 (9), t018 (5), t021 (5), t233 (2), singletons (5) |
| CC22 | 19 (14.3) | t3243 (10), t223 (5), t005 (2), singletons (2) |
| CC398 | 14 (10.6) | t6605 (5), t1149 (4), t937 (3), t571 (2) |
| CC45 | 13 (9.8) | t630 (4), singletons (9) |
| CC8 | 12 (9.1) | t701 (5), t008 (3), singletons (4) |
| CC1 | 11 (8.3) | t189 (5), t127 (4), singletons (2) |
| CC5 | 7 (5.3) | t002 (3), t111 (2), singletons (2) |
| CC15 | 4 (3) | t084 (3), t228 (1) |
| CC9 | 4 (3) | t209 (3), t099 (1) |
| CC72 | 4 (3) | t148 (4) |
| CC7 | 4 (3) | t091 (2), singletons (2) |
| CC20 | 3 (2.2) | t164 (2), t731 (1) |
| Other | t12793 (2), t1445 (4), t1451 (2), t1458 (3), t14581 (2), t2325 (3), t267 (3), t3454 (10), t377 (2), t493 (3), t7234 (2), t364 (2), t773 (5), singletons (74) |
Maternal S. aureus carriage patterns.
At recruitment, 80 women carried S. aureus in the nose, and 28 carried S. aureus in the vagina. A total of 22 women carried S. aureus in both the nose and the vagina, and 17 of these women carried the same strain in both sites. We found that 57 women carried S. aureus in at least one site at both recruitment and immediately surrounding labor. In 54 cases (91.2%), the same strain was carried during gestation and labor, regardless of the carriage site (Table 3).
TABLE 3.
Maternal and infant carriage patterns and dynamics
| Variablea | Description | No. | % | Range | Mean (SD) |
|---|---|---|---|---|---|
| Mother | 130 | ||||
| Carriage site at recruitment | Vaginal only | 28 | 21.54 | ||
| Nasal only | 80 | 61.54 | |||
| Nasal and vaginal | 22 | 16.92 | |||
| Carriage persistence | Transient | 32 | 24.62 | ||
| Undetermined | 28 | 21.54 | |||
| Persistent | 70 | 53.85 | |||
| No. of strains carried in yr (vagina + nose) | 1–4 | 1.42 (±0.69) | |||
| Child | |||||
| Nasal/rectal carriage | First 72 h of life | 23 | 23.26 | ||
| First mo | 85 | 64.39 | |||
| First yr | 123 | 93.18 | |||
| Maternal strain carriage | First 72 h of life | 15/22 | 68.18 | ||
| First mo | 52/79 | 65.82 | |||
| During first yr | 79/123 | 64.23 | |||
| Persistent carriage | 17 | 12.88 | |||
| No. of strains carried in yr (rectum + nose) | 1–4 | 1.44 (± 0.70) |
Variables with nonsignificant (P < 0.2) results in univariate model: antibiotic use in the preceding month.
Most of the participating women were defined as persistent carriers (n = 70, 53.9%), while nearly a quarter were transient carriers (n = 32, 24.6%), and for an additional 28 women it was difficult to determine the pattern of carriage since they were carriers approximately 50% of the time (Table 3). Of the 70 persistent-carrier women, 49 (70%) carried a single strain along all screenings during the year, as defined by PFGE or spa type, while 21 (30%) women carried a second strain at some point during the year. Nine of these women carried the secondary strain for only a month or two, after which the primary strain was again detected, while six women exchanged their initial strain with a second strain that was carried for most of the follow-up visits, and four women replaced their primary strain with a second strain that was carried for an extended period (Fig. 1a). No relationship was found between the length of carriage of a transient strain and its genetic relatedness to the persistent strain.
FIG 1.
Patterns of carriage among mothers. (a) Carriage patterns of persistent carrier mothers (n = 70); (b) carriage patterns of transient carrier mothers (n = 32). Green strain indicates the main strain carried by the mother. Blue indicates the secondary strain carried by the mother. Yellow and red indicate third and fourth strains carried, when applicable. Gray indicates a missed screen or unidentified strain.
Of the women defined as transient carriers (n = 32), 15 (46.9%) never carried S. aureus during the year, apart from the initial screening when recruited during pregnancy. Of the transient carrier women who carried S. aureus in more than one visit, 5/15 (33.3%) carried two different strains in the different visits (Fig. 1b).
Infant S. aureus acquisition and patterns.
Within the first year of life, 123 (93%) of the infants acquired S. aureus. Thirty (23% newborns acquired S. aureus and carried it in at least one body site (nose, rectum, ear, or umbilicus) within the first days of life, before discharge from the hospital. Twenty-three of them (76.7%) carried it in the nose or rectum. Initially, infant carriage was evenly distributed between nasal and rectal carriage. At 1 month, 84.2% were nasal carriers, and 47.4% were both nasal and rectal carriers. With time, rectal carriage prevalence decreased and the nose became the predominant site. (Fig. 2). Over half of the infants (n = 67) carried both a rectal and nasal strain in the same month at some point over the course of the year. The nasal and rectal strains were genetically identical in 85% (57/67) of the screens in which S. aureus was isolated from both sites.
FIG 2.
Infant nasal and rectal S. aureus carriage by month. Bars represent the percentages of all screened children who carried S. aureus nasally (black), rectally (dark gray), and both rectally and nasally (light gray) in a given month.
Of the 23 children that acquired S. aureus in the nose or rectum in the first days of life for whom strain data were available, 15 (68.2%) acquired the maternal strain (Table 3). On the first month visit, 61.8% (n = 76) of infants were S. aureus carriers, 52 (72.2%) of them carried the maternal strain at this point.
None of the isolates carried by the mothers during the whole follow-up period were methicillin resistant S. aureus (MRSA). Two infants acquired carriage of nonmaternal MRSA strains soon after birth, during their stay in the hospital, but both replaced their strains in the next month, one with the maternal strain, and one with a different, unrelated strain.
Four patterns of carriage could be identified in the infants: (i) “persistent carriers” (n = 17, 13%), i.e., those who carried S. aureus at least 66% of screenings but also at least 50% of the screenings in the second half of the year; (ii) “never carriers,” infants who did not acquire S. aureus during the whole study period (n = 9, 7%) despite the mother being a carrier upon enrollment; (iii) “transient carriers,” infants who carried S. aureus for <34% of the screenings (n = 55, 42%); and (iv) finally a group with an undetermined pattern (n = 51, 38%), who did not meet the criteria for any of the above carriage patterns (Fig. 3).
FIG 3.
Infant carriage patterns. (a) Carriage patterns of persistent carrier infants (n = 17); (b) carriage patterns of transient carrier infants (n = 52). Green strain indicates the main strain carried by the infant’s mother. Blue indicates the secondary strain, acquired by the child from a different source. Yellow and red indicate third and fourth strains carried, when applicable. Gray indicates a missed screen.
Most persistent-carrier infants carried a single strain over the course of the year, similar to the observation in the mother population. Over 70% (12/17) of these infants persistently carried the maternal strain (Fig. 3), whereas five (29.4%) carried a strain that was different than the strain isolated from their mother. In four of these five cases, the mother never carried the infant’s persistent strain.
Of the nine infants who were never carriers, three had a persistent carrier mother. Three of the mothers of the never carriers only carried S. aureus in the vagina and not in the nose at recruitment and birth, and another five mothers carried S. aureus in the nose at recruitment but screened negative for nasal carriage at birth and/or the first month of follow-up.
The most common pattern observed among mothers and infants was that in which the primary maternal strain was carried by both the mother and the infant (n = 76, 58%). In 28 cases (21.5%), the infant did not acquire the maternal strain at any point during the year.
No difference was observed between the number of strains carried by the mother and baby throughout the year (Table 3). Most mother-infant dyads (85%) shared a strain at least once during the year.
Having a persistent-carrier mother was more common among persistent-carrier infants (58.8%), compared to transient-carrier infants (49.1%) or to never-carrier infants (33.3%). However, having a persistent-carrier mother was not an independent predictor for infant carriage persistence, as determined in a univariate analysis (P = 0.38).
Predictors of S. aureus carriage during the first year of life.
The significant independent predictors for carriage in any given month were age, carriage of S. aureus in the previous month, and maternal carriage in the previous month (Table 4). The major independent predictor for an infant to be a persistent carrier was early acquisition of S. aureus, i.e., before the age of 2 months (Table 5). Furthermore, when assessing the association between the time of first S. aureus acquisition and the duration of carriage, we observed that the time of first acquisition predicts the duration of the carriage; The earlier the first acquisition, the longer it was carried (r = –0.3, P = 0.0007) (Fig. 4). Although children who acquired the first strain during the first 2 months of life carried it for an average of 3.68 ± 2.42 months (range, 1 to 12 months; median, 3 months), all of the children that acquired the first strain after the age of 4 months had very short-lived carriage (range, 1 to 4 months; median, 1 month).
TABLE 4.
Independent predictors of child S. aureus carriage in each month
| Variablea | OR | 95% CI | P |
|---|---|---|---|
| Child S. aureus carriage in previous mo | 3.11 | 2.28–4.26 | <0.0001 |
| Mother S. aureus carriage in previous mo | 1.98 | 1.41–2.78 | 0.0001 |
| Age (mo) | 270.35 | 82.34–887.76 | <0.0001 |
| DCC attendance in previous mo | 0.72 | 0.45–1.16 | 0.18 |
| Breastfeeding in previous mo | 0.73 | 0.49–1.09 | 0.12 |
Variables with nonsignificant (P < 0.2) results in univariate model: antibiotic use in the preceding month.
TABLE 5.
Independent predictors of persistent S. aureus carriage in infants
| Variablea | OR | 95% CI | P |
|---|---|---|---|
| Early acquisition (<2 mo) | 26.649 | 2.944–241.24 | 0.0035 |
| DCC attendance (yes/no) | 0.238 | 0.07–0.85 | 0.0271 |
| Breastfeeding | 0.313 | 0.055–1.771 | 0.1891 |
| Maternal carriage in the first mo | 3.18 | 0.525–19.261 | 0.2081 |
Variables with nonsignificant (P < 0.2) results in univariate model: sex, gestational age, birth weight, pets, antibiotics in first year of life, skin infections, and maternal carriage persistence.
FIG 4.
First acquisition of carriage versus duration of initial carriage. Circle size indicates the amount of infants whose acquisition versus duration intersect at that point. The shaded area indicates the maximum possible observable duration left after that point.
DCC attendance was negatively associated with persistent S. aureus carriage in children (P = 0.03). Sex, gestational age, maternal carriage persistence, birth weight, breastfeeding, pets, antibiotic use in the first year of life, and skin infections were included in the univariate analysis but were not found to be significant and were not included in the multivariate analysis.
DISCUSSION
In this study, we followed maternal and infant S. aureus carriage throughout the first year of life. Although mothers were recruited at a monitoring unit, where high-risk pregnancies are followed, we have previously shown that carrier and noncarrier women recruited in this unit were similar with regard to demographic and pregnancy/labor variables (17).
We found that most infants (93%) acquired S. aureus sometime during the first year; however, most did not acquire S. aureus during birth but acquired the maternal strain within the first month of life. Furthermore, we found that early acquisition of a S. aureus strain is the most significant predictor of long and persistent S. aureus carriage in the first year of life. Previous studies have proposed that S. aureus transmission in infants may be due to the presence of S. aureus on nipples and acquisition through breastfeeding (18, 19), but while we did not screen the mothers’ nipples, we did not find breastfeeding to be a predictor of infant carriage. In addition, Le Thomas et al. (18) observed that the strains found in breastmilk were identical to those found in parental nasal samples. These results point to the significant impact of maternal S. aureus carriage in the first months of a child life on the infant’s carriage dynamics.
We show that over half of the mothers who were detected as carriers around labor persistently carried S. aureus, mostly with a single strain throughout the year. A quarter of the mothers were defined as transient carriers, of whom most carried S. aureus in only one or two carriage events. In line with previous studies, we observed strain persistence in our healthy adult population (12, 20). MRSA was not isolated from any mother at any point throughout the year. This is consistent with data from Israel, where community-acquired MRSA is not common (21).
In contrast to the extensive data on adult S. aureus carriage, not much has been reported on carriage patterns in early infancy. The duration of carriage, the patterns and dynamics of carriage, or the predictors of carriage during infancy have been studied, but most studies did not continue past 6 months of age (22, 23), and those that followed the infants and mothers for an entire year only looked at two to three swabs during the course of the year (6, 24). Here, we screened the mothers and infants monthly to obtain a full picture of their carriage patterns, as well as predictors of infant carriage in each month.
We previously reported that infants born to carrier mothers in the same cohort acquired their maternal strain in the first month of life (17). Here, we looked at the full year and found that throughout the course of the year, 85% of the infants acquired the maternal strain at least once and that 12 of 17 persistent infants carried the maternal strain persistently. In line with observations by Jimenez-Truque et al. (22), we observed that maternal carriage was a predictor of infant carriage at any given month but, surprisingly, we did not find maternal persistence to be an independent predictor of infant persistence. Rather, it appeared that persistent carrier infants were likely to acquire their maternal strain early, within the first 1 to 2 months of life, and that this early acquisition was the most significant predictor of persistent carriage, typically of a single strain, i.e., the maternal strain. Furthermore, we found that 33% of never-carrier infants were born to persistent mothers; this is low compared to persistent-carrier infants, 70% of whom had a persistent-carrier mother. In addition, we and others have previously found that infants carried or were infected by strains carried by both parents (18, 19, 21), and it is likely that looking at parental carriage patterns, as opposed to only maternal, would provide more evidence of an association between parent and infant persistence.
The sites of S. aureus carriage in early infancy have not been thoroughly studied previously. Here, we screened infants for both rectal and nasal carriage and observed that while prevalences of rectal and nasal carriage were almost equal surrounding birth, nasal carriage became the dominant site of carriage. We also observed that rectal and nasal strains were identical 85% of the time. In line with this, Lindberg et al. (19) observed that strains isolated from rectal samples in the first 2 months of life were parental skin strains.
The role of the pathogen in determining the carriage pattern has been previously studied. No association between specific clones and carriage pattern was found by Muthukrishnan et al. (13). Similarly, we did not find any correlation between specific strains (as determined by spa type) and carriage pattern in our population. Furthermore, we assessed whether, among individuals that carried a secondary strain, the duration of carriage of the secondary strain would depend on the genetic relatedness to the primary strain, but we did not find any statistically significant relation.
Previous findings by our group show that S. aureus carriers display a tolerogenic immune response to their own strain (25), and it is known that host-bacterium interactions in early life help shape the developing immune system and the commensal microbiome for years to come. These results, where we show that early acquisition of a strain predicts longer carriage during the first year of life, are consistent with the idea of a tolerogenic response to early acquisition of S. aureus, although long-term follow-up into late childhood or even adulthood are required to determine the implications of early S. aureus acquisition.
Our study has several limitations. Although this study was large and comprehensive, a larger population, one possibly including follow-up with noncarriers, could provide greater statistical power to some predictors and correlations. We used conventional screening using cotton swabs. Potentially, adding an enrichment step could have increased our yield of detection. However, our carriage rates among mothers were similar to previously published adult carrier rates. In addition, our results on genetic identity depend solely on the evolution of the spa gene.
Some potential predictors were not or could not be assessed in our study. (i) The role of other family members was not assessed. (ii) The role of microbial interference by the child microbiome was not assessed. Various bacterial species were shown to interact with S. aureus in vitro and in vivo (25–28). Thus, studies to understand the role of the microbiome in determining S. aureus carriage patterns are required. (iii) While breastfeeding was assessed, the study was probably underpowered due to the high proportion of breastfeeding (>90%). Theoretically, breastfeeding could play a role, either as protective, via antibodies from the mother, or as a risk factor for the baby due to intensive contact with the mother.
Since S. aureus carriage plays such a significant role in the dynamics of infection, understanding the initial acquisition is vital. This study is the first to show the prominent role of early strain acquisition in both carriage duration and pattern, as well as in the intimate dynamics of S. aureus carriage between mothers and babies.
ACKNOWLEDGMENTS
We thank Eyal Leshem, who was involved in the early stages of the project, and Yael Beker-Ilany, who was devoted to the women and the children and carried out the monthly visits along most of the study years. We also thank the helpful Sheba Medical Center monitoring unit team and the nursery team.
This study was funded by the Chief Scientist, Ministry of Health, Israel (grant 3-00000-5622), and by the Israel Science Foundation (grants 1590/09 and 1658/15).
REFERENCES
- 1.von Eiff C, Becker K, Machka K, Stammer H, Peters G. 2001. Nasal carriage as a source of Staphylococcus aureus bacteremia. N Engl J Med 344:11–16. doi: 10.1056/NEJM200101043440102. [DOI] [PubMed] [Google Scholar]
- 2.Kluytmans J, Wertheim H. 2005. Nasal carriage of Staphylococcus aureus and prevention of nosocomial infections. Infection 33:3–8. doi: 10.1007/s15010-005-4012-9. [DOI] [PubMed] [Google Scholar]
- 3.Williams R. 1963. Healthy carriage of Staphylococcus aureus: its prevalence and importance. Bacteriol Rev 27:56. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Bogaert D, van Belkum A, Sluijter M, Luijendijk A, de Groot R, Rümke H, Verbrugh H, Hermans P. 2004. Colonization by Streptococcus pneumoniae and Staphylococcus aureus in healthy children. Lancet 363:1871–1872. doi: 10.1016/S0140-6736(04)16357-5. [DOI] [PubMed] [Google Scholar]
- 5.Zanger P, Nurjadi D, Gaile M, Gabrysch S, Kremsner PG. 2012. Hormonal contraceptive use and persistent Staphylococcus aureus nasal carriage. Clin Infect Dis 55:1625–1632. doi: 10.1093/cid/cis778. [DOI] [PubMed] [Google Scholar]
- 6.Lebon A, Labout JA, Verbrugh HA, Jaddoe VW, Hofman A, van Wamel W, Moll HA, van Belkum A. 2008. Dynamics and determinants of Staphylococcus aureus carriage in infancy: the Generation R Study. J Clin Microbiol 46:3517–3521. doi: 10.1128/JCM.00641-08. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Jacoby P, Carville KS, Hall G, Riley TV, Bowman J, Leach AJ, Lehmann D, Team KOMRP. 2011. Crowding and other strong predictors of upper respiratory tract carriage of otitis media-related bacteria in Australian Aboriginal and non-Aboriginal children. Pediatr Infect Dis J 30:480–485. doi: 10.1097/INF.0b013e318217dc6e. [DOI] [PubMed] [Google Scholar]
- 8.Kluytmans J, van Belkum A, Verbrugh H. 1997. Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks. Clin Microbiol Rev 10:505–520. doi: 10.1128/CMR.10.3.505. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9.Geoghegan JA, Irvine AD, Foster TJ. 2018. Staphylococcus aureus and atopic dermatitis: a complex and evolving relationship. Trends Microbiol 26:484–497. doi: 10.1016/j.tim.2017.11.008. [DOI] [PubMed] [Google Scholar]
- 10.Conceição T, de Lencastre H, Aires-de-Sousa M. 2017. Carriage of Staphylococcus aureus among Portuguese nursing students: a longitudinal cohort study over four years of education. PLoS One 12:e0188855. doi: 10.1371/journal.pone.0188855. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Sakwinska O, Blanc DS, Lazor-Blanchet C, Moreillon M, Giddey M, Moreillon P. 2010. Ecological temporal stability of Staphylococcus aureus nasal carriage. J Clin Microbiol 48:2724–2728. doi: 10.1128/JCM.02091-09. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.VandenBergh MFQ, Yzerman EPF, van Belkum A, Boelens HAM, Sijmons M, Verbrugh HA. 1999. Follow-up of Staphylococcus aureus nasal carriage after 8 years: redefining the persistent carrier state. J Clin Microbiol 37:3133–3140. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Muthukrishnan G, Lamers RP, Ellis A, Paramanandam V, Persaud AB, Tafur S, Parkinson CL, Cole AM. 2013. Longitudinal genetic analyses of Staphylococcus aureus nasal carriage dynamics in a diverse population. BMC Infect Dis 13:221. doi: 10.1186/1471-2334-13-221. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Murchan S, Kaufmann ME, Deplano A, de Ryck R, Struelens M, Zinn CE, Fussing V, Salmenlinna S, Vuopio-Varkila J, El Solh N, Cuny C, Witte W, Tassios PT, Legakis N, van Leeuwen W, van Belkum A, Vindel A, Laconcha I, Garaizar J, Haeggman S, Olsson-Liljequist B, Ransjo U, Coombes G, Cookson B. 2003. Harmonization of pulsed-field gel electrophoresis protocols for epidemiological typing of strains of methicillin-resistant Staphylococcus aureus: a single approach developed by consensus in 10 European laboratories and its application for tracing the spread of related strains. J Clin Microbiol 41:1574–1585. doi: 10.1128/jcm.41.4.1574-1585.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Tenover FC, Arbeit RD, Goering RV, Mickelsen PA, Murray BE, Persing DH, Swaminathan B. 1995. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J Clin Microbiol 33:2233–2239. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 16.Harmsen D, Claus H, Witte W, Rothgänger J, Claus H, Turnwald D, Vogel U. 2003. Typing of methicillin-resistant Staphylococcus aureus in a university hospital setting by using novel software for spa repeat determination and database management. J Clin Microbiol 41:5442–5448. doi: 10.1128/JCM.41.12.5442-5448.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 17.Maayan-Metzger A, Strauss T, Rubin C, Jaber H, Dulitzky M, Reiss-Mandel A, Leshem E, Rahav G, Regev-Yochay G. 2017. Clinical evaluation of early acquisition of Staphylococcus aureus carriage by newborns. Int J Infect Dis 64:9–14. doi: 10.1016/j.ijid.2017.08.013. [DOI] [PubMed] [Google Scholar]
- 18.Le Thomas I, Mariani-Kurkdjian P, Collignon A, Gravet A, Clermont O, Brahimi N, Gaudelus J, Aujard Y, Navarro J, Beaufils F, Bingen E. 2001. Breast milk transmission of a Panton-Valentine leukocidin-producing Staphylococcus aureus strain causing infantile pneumonia. J Clin Microbiol 39:728–729. doi: 10.1128/JCM.39.2.728-729.2001. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Lindberg E, Adlerberth I, Hesselmar B, Saalman R, Strannegård I-L, Åberg N, Wold AE. 2004. High rate of transfer of Staphylococcus aureus from parental skin to infant gut flora. J Clin Microbiol 42:530–534. doi: 10.1128/jcm.42.2.530-534.2004. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20.Chen C-J, Wang S-C, Chang H-Y, Huang Y-C. 2013. Longitudinal analysis of methicillin-resistant and methicillin-susceptible Staphylococcus aureus carriage in healthy adolescents. J Clin Microbiol 51:2508. doi: 10.1128/JCM.00572-13. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Regev-Yochay G, Raz M, Carmeli Y, Shainberg B, Navon-Venezia S, Pinco E, Leavitt A, Keller N, Rahav G, Malley R, Rubinstein E. 2009. Parental Staphylococcus aureus carriage is associated with staphylococcal carriage in young children. Pediatr Infect Dis J 28:960–965. doi: 10.1097/INF.0b013e3181a90883. [DOI] [PubMed] [Google Scholar]
- 22.Jimenez-Truque N, Tedeschi S, Saye EJ, McKenna BD, Langdon W, Wright JP, Alsentzer A, Arnold S, Saville BR, Wang W, Thomsen I, Creech CB. 2012. Relationship between maternal and neonatal Staphylococcus aureus colonization. Pediatrics 129:e1252–e1259. doi: 10.1542/peds.2011-2308. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23.Peacock SJ, Justice A, Griffiths D, De Silva G, Kantzanou M, Crook D, Sleeman K, Day NP. 2003. Determinants of acquisition and carriage of Staphylococcus aureus in infancy. J Clin Microbiol 41:5718–5725. doi: 10.1128/jcm.41.12.5718-5725.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.Schaumburg F, Alabi AS, Mombo-Ngoma G, Kaba H, Zoleko RM, Diop DA, Mackanga J-R, Basra A, Gonzalez R, Menendez C, Grobusch MP, Kremsner PG, Köck R, Peters G, Ramharter M, Becker K. 2014. Transmission of Staphylococcus aureus between mothers and infants in an African setting. Clin Microbiol Infect 20:O390–O396. doi: 10.1111/1469-0691.12417. [DOI] [PubMed] [Google Scholar]
- 25.Uehara Y, Nakama H, Agematsu K, Uchida M, Kawakami Y, Fattah AA, Maruchi N. 2000. Bacterial interference among nasal inhabitants: eradication of Staphylococcus aureus from nasal cavities by artificial implantation of Corynebacterium sp. J Hospital Infection 44:127–133. doi: 10.1053/jhin.1999.0680. [DOI] [PubMed] [Google Scholar]
- 26.Iwase T, Uehara Y, Shinji H, Tajima A, Seo H, Takada K, Agata T, Mizunoe Y. 2010. Staphylococcus epidermidis Esp inhibits Staphylococcus aureus biofilm formation and nasal colonization. Nature 465:346. doi: 10.1038/nature09074. [DOI] [PubMed] [Google Scholar]
- 27.Regev-Yochay G, Trzcinski K, Thompson CM, Malley R, Lipsitch M. 2006. Interference between Streptococcus pneumoniae and Staphylococcus aureus: in vitro hydrogen peroxide-mediated killing by Streptococcus pneumoniae. J Bacteriol 188:4996–5001. doi: 10.1128/JB.00317-06. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 28.Lewnard JA, Givon-Lavi N, Huppert A, Pettigrew MM, Regev-Yochay G, Dagan R, Weinberger DM. 2016. Epidemiological markers for interactions among Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus in upper respiratory tract carriage. J Infect Dis 213:1596–1605. doi: 10.1093/infdis/jiv761. [DOI] [PMC free article] [PubMed] [Google Scholar]