Screening of Clostridioides difficile carriers in an urban academic medical center: understanding implications of disease

Abstract

Objective:

Efforts to reduce C. difficile infections have targeted transmission from patients with symptomatic C. difficile. However, many patients with the C. difficile organism are carriers without symptoms who may serve as reservoirs for spread of infection and may be at risk for progression to symptomatic C. difficile. To estimate the prevalence of C. difficile carriage and determine the risk and speed of progression to symptomatic C. difficile among carriers, we established a pilot screening program in a large urban hospital.

Design:

Prospective cohort study

Setting:

An 800-bed, tertiary-care, academic medical center in the Bronx, NY

Participants:

A sample of admitted adults without diarrhea, with oversampling of nursing facility patients

Methods:

Perirectal swabs were tested by Polymerase Chain Reaction for C. difficile within 24 hours of admission, and patients were followed for progression to symptomatic C. difficile. Development of symptomatic C. difficile was compared among C. difficile carriers and non-carriers using a Cox proportional hazards model.

Results:

Of the 220 subjects, 21 (9.6%) were C. difficile carriers, including 10.2% of the nursing facility residents and 7.7% of the community residents (p=0.60). Among the 21 C. difficile carriers, 8 (38.1%) progressed to symptomatic C. difficile while only 4 (2.0%) of the 199 non-carriers progressed to symptomatic C. difficile (p<0.0001; Hazard Ratio 23.9, 95% CI 7.2-79.6).

Conclusions:

Asymptomatic carriage of C. difficile is prevalent among admitted patients and confers a significant risk of progression to symptomatic C. difficile infection. Screening for asymptomatic carriers may represent an opportunity to reduce C. difficile infections.

Introduction

There are over 400,000 cases and almost 30,000 deaths from Clostridioides difficile(C. difficile)-associated diarrhea in the United States annually.[1] Efforts to reduce the spread of C. difficile have focused on reducing transmission from patients with symptomatic C. difficile associated diarrhea.[2 3] However, many patients are C. difficile carriers who do not have diarrhea. Asymptomatic carriers may serve as a reservoir and spread C. difficile to those around them.[4-7] However, patients who are carriers are not routinely identified on hospital admission. In addition, though some research suggested that asymptomatic carriage is protective against symptomatic C. difficile,[8] other studies demonstrated that patients can progress from carrier state to symptomatic C. difficile infection.[9] There is limited data demonstrating how frequently and how quickly this occurs.[10] Therefore, identification of asymptomatic carriers could reduce the spread of C. difficile through two mechanisms: first, isolation of C. difficile carriers could reduce transmission to uninfected patients and, second, interventions targeting C. difficile carriers could potentially prevent progression to symptomatic C. difficile.

C. difficile is a spore-forming, Gram-positive anaerobic bacillus spread by fecal-oral transmission of spores, which remain viable for long periods of time ex-vivo.[11 12] Though C. difficile carriers do not have diarrhea, they do shed spores that can contaminate environmental surfaces.[4] While it remains unknown what proportion of symptomatic infection results from transmission from asymptomatic carriers, research indicates that this does occur.[13]

Previously, C. difficile carriage was thought to be protective against the future development of symptomatic C. difficile,[8] and progression was understood to be rare. However, recent evidence suggests otherwise.[6 13-16] Progression to symptomatic C. difficile often follows acquired immunocompromise (e.g. steroids or severe illness) or administration of antibiotics which disrupt the gut flora.[17] Both are frequently encountered in hospitalized patients. Hospitals are responsible for reporting “healthcare facility-onset” C. difficile,[18] diagnosed 3 days or more after hospital admission, which does not account for symptoms or carrier status before the admission. Identifying a high rate of progression from C. difficile carrier to symptomatic C. difficile could change what we consider a “Hospital Acquired Infection,” especially if the bacteria was not necessarily acquired in the hospital, but was present on admission and only the diarrhea began in the hospital.

To estimate the prevalence of asymptomatic C. difficile carriage at the time of hospital admission and determine the rate and time to progression to symptomatic C. difficile infection, we tested and prospectively followed asymptomatic patients being admitted with no diarrhea. The objectives of our two-part study were first to identify asymptomatic C. difficile carriers and second to observe carriers and non-carriers for progression to symptomatic C. difficile. We hypothesized that 1) admission from a nursing facility would be positively associated with C. difficile carriage and that 2) asymptomatic C. difficile carriers would be at increased risk for developing symptomatic C. difficile compared to asymptomatic non-carriers.

Methods

Study Design and Setting

We performed a prospective cohort study on a sample of patients being admitted to a large university hospital in the Bronx, NY, between July 2017 and March 2018. The hospital contains over 800 beds and receives over 45,000 hospital admissions annually. To determine the prevalence of C. difficile carriage, patients being admitted to the hospital without diarrhea were tested for C. difficile. To follow these patients prospectively, we utilized our unified electronic medical record shared among multiple hospitals and outpatient clinics in the health system. All patients were followed within our system for 6 months or until death for the subsequent diagnosis of symptomatic C. difficile infection.

Participants

All patients with an admission order from July 2017 to March 2018 were eligible for inclusion. During the study period a convenience sample of days including weekends, was used for screening and testing. On screening days, all patients admitted within the previous 24 hours from a nursing facility were approached for inclusion. On those same days, a worklist was generated, and any patient admitted from the community within the previous 24 hours was assigned a number. Random number generators were used to determine a random sample of community patients. Because previous studies suggest that nursing facility residents have a high prevalence of C. difficile carriage, patients from the community were sampled in a 1 to 4 ratio with patients from nursing facilities. For inclusion in the study, subjects were ≥21 years old and required an admission order from the Emergency Department within the previous 24 hours. The research team queried any patient, family, or staff and excluded patients with active diarrhea defined as ≥3 episodes of loose stool in the previous 24 hours or ≥2 episodes in the previous 12 hours. Subjects were excluded if there was documentation of comfort care only status, if they had a colostomy, or if they were admitted to the Pediatrics, Obstetric/Gynecologic, or Psychiatry Services.

Because screening admitted patients for infectious diseases is part of standard Infection Prevention and Control practice, we did not seek consent from each study subject, but offered the option of dissenting (declining) when approached for participation. Following testing, participants were observed for 6 months or until death. The Montefiore/Einstein Institutional Review Board approved the study, granting a waiver of informed consent.

Data Collection Methods

Eligible subjects underwent swabbing of their peri-rectal area with an ESwab™ collection and transport system by a single member of the study team. No invasive rectal swabbing was performed. Rectal swabbing or direct testing of stool specimens are the accepted clinical standards, but previous studies have demonstrated the utility of perirectal swabbing.[19] If stool was available, a separate swab was performed directly on stool. Test swab soilage, as defined by any visible material on the swab, was recorded as recommended.[19]

Specimens were processed by the study team (SB and DD) on the same day as collection. Two testing methodologies were used for all specimens: 1) C. difficile Quik Chek Complete^® (Abbott) to test for Glutamate Dehydrogenase (GDH) and Toxins A and B and 2) XPert^® C. difficile/Epi (Cepheid) real-time Polymerase Chain Reaction (PCR) assay which detects the Toxin B gene.[20 21] All specimens were also tested by toxigenic culture using spore enriched specimens in cultures with selective Chopped Meat Broth incubated for 48-72 hours followed by repeat GDH and Toxin A/B testing.[22 23]

Demographic and clinical characteristics were extracted from the Electronic Medical Record which included all inpatient and outpatient visits and lab tests sent from the medical center.

Measures

Prevalence Analysis

Determination of active diarrhea status was queried directly of patients, family, or staff. All other demographic and clinical characteristics were recorded from the electronic medical record or an extracted replicate of the electronic medical record. C. difficile carrier status was defined as any positive PCR or Toxin test or toxigenic culture for C. difficile without diarrhea (diarrhea was an exclusion criterion). If the primary clinical team ordered a subsequent C. difficile test, they were informed of any positive study testing result but otherwise were unaware of subject participation in the study. This allowed for the possibility of direct benefit to subjects in the form of hastened diagnosis and treatment. Independent variables examined included age, gender, nursing facility or community resident, season of enrollment, soilage of the test swab, previous admissions within 28 days,[18] previous antibiotics within 90 days,[24] and previous C. difficile infection within 56 days.[18]

Outcomes Analysis

The primary outcome, symptomatic C. difficile infection, was defined as any positive clinical test for C. difficile sent by the primary clinical team as part of usual care. The microbiology laboratory rejects solid stool specimens, so the presence of diarrhea in patients was assumed. The clinical algorithm used in this healthcare system, in accordance with guidelines,[18] is a combined GDH and Toxin test (Quik Chek Complete^®) followed by PCR (XPert^®) if the GDH and Toxin results are discrepant. We compared time to C. difficile positive testing among carriers versus non-carriers, censored at 6 months or death.

Statistical Analysis

Baseline characteristics of nursing facility residents versus community residents were compared using Chi-squared and Fisher’s exact tests as appropriate. We calculated the prevalence of asymptomatic C. difficile carriage in the overall study population, in nursing facility residents, and community residents. The significance of the difference in prevalences was tested using a Chi-squared test and univariate logistic regression model. The time of progression to symptomatic C. difficile infection or death, censored at 6 months, was plotted for carriers and non-carriers using the method of Kaplan and Meier, and a log-rank test was used to test the differences between groups. Finally, a univariate Cox-proportional hazards model was constructed to estimate the hazard of progressing to symptomatic infection in carriers versus non-carriers. Given the small number of outcome events, no multivariate analyses were performed.

Statistical analysis was performed using STATA software, version 14.2. P values less than 0.05 were considered statistically significant.

Results

Of the 351 potential subjects evaluated for inclusion, 220 subjects were enrolled (62.7%). Common reasons for non-enrollment included: declined participation (30), discharged before testing (28), and excluded due to diarrhea (14). Twenty-eight patients were not eligible for 7 additional reasons based on the exclusion criteria. Thirty-one patients were included in random sampling, and thus in the potential subject pool, but they were never approached for inclusion to maintain the 4 to 1 sampling strategy. In terms of acceptability to the subjects, only 30/351 (8.5%) of all eligible subjects declined participation.

Of the 220 enrolled subjects, most were female (54%), ≥65 years old (67%), enrolled in the summer (58%), did not have a soiled test swab (55%), and were nursing facility residents (76%), in accordance with the 4 to 1 enrollment strategy. The characteristics of the total study population and the nursing facility and community residents are presented in Table 1.

Table 1:

Characteristics of Population by Nursing Facility versus Community residence and Population as a whole

	Nursing Facility Residents n=168, n(%)	Community Residents n=52, n(%)	p-value*	Total Populationϴ n=220, n(%)
Age			<0.001
<65 years	40 (23.8%)	32 (61.5%)		72 (32.7%)
≥65 years	128 (76.2%)	20 (38.5%)		148 (67.3%)
Gender			p=0.78
Female	91 (54.2%)	27 (51.9%)		118 (53.6%)
Male	77 (45.8%)	25 (48.1%)		102 (46.4%)
Race/Ethnicity			p=0.09
White	24 (14.3%)	3 (5.8%)		27 (12.3%)
Black	66 (39.3%)	15 (28.9%)		81 (36.8%)
Hispanic	52 (31.0%)	24 (46.2%)		76 (34.5%)
Unknown/Other	26 (15.5%)	10 (19.2%)		36 (16.4%)
Season			p=0.70
Summer	99 (58.9%)	28 (53.8%)		127 (57.7%)
Winter	19 (11.3%)	8 (15.4%)		27 (12.3%)
Spring	50 (29.8%)	16 (30.8%)		66 (30.0%)
Soiled test swabβ	85 (50.9%)	14 (26.9%)	p=0.002	99 (45.2%)
Previous Admission	49 (29.2%)	7 (13.5%)	p=0.023	56 (25.5%)
Previous Antibiotics	64 (38.1%)	12 (23.1%)	p=0.047	76 (34.5%)
C. difficile carrierβ	17 (10.2%)	4 (7.7%)	p=0.60	21 (9.6%)
Positive by Toxinβ¥	3 (1.6%)	0 (0%)	p=1.00	3 (1.4%)

^*Bold typeface indicates p-value less than 0.05

^βIndicates that data is calculated based on 219 subjects total (missing data on one subject)

^¥Fisher’s exact test used

^ϴUnadjusted statistics on total population

Prevalence Analysis

Of 220 subjects tested, 21 (9.6%) were asymptomatic C. difficile carriers, which included 17 of 168 nursing facility residents tested (10.2%), and 4 of 52 community residents tested (7.7%), a difference that was not significant (p=0.60).

The associations between subject demographic and clinical characteristics and the odds of asymptomatic carriage are presented in Table 2. Having a soiled swab was significantly associated with carriage (OR= 2.7, 95% CI: [1.03-6.9]; p=0.04). In addition, previous antibiotic exposure was non-significantly associated with asymptomatic carriage (OR=2.3, 95% CI: 0.9-5.6; p=0.08).

Table 2:

Odds Ratios for being a C. difficile carrier

	Odds Ratio	CI 95 of Odds Ratio	p value
Nursing Facility	1.4	0.4 – 4.2	0.60
Male Gender	1.06	0.4 – 2.6	0.90
Age ≥ 65 years	1.6	0.6 – 4.6	0.36
Soiled Swab	2.7	1.03 – 6.9	0.04
Summer Enrollment	1.0	ref
Winter Enrollment	0.4	0.05 – 3.1	0.34
Spring Enrollment	1.3	0.5 – 3.5	0.54
Previous Admission	1.2	0.4 – 3.2	0.74
Previous Antibiotics	2.3	0.9 – 5.6	0.08

Outcomes Study

Among 21 subjects identified as C. difficile carriers, 8 (38.1%) progressed to clinical C. difficile infection within 6 months. Among 199 subjects who were not carriers at enrollment, 4 (2.0%) developed symptomatic C. difficile infection within 6 months. Most carriers that progressed to symptomatic C. difficile infection did so within 2 weeks of enrollment (n.b. patients were assessed and excluded if diarrhea was present at enrollment). In the time-to-event analysis, C. difficile carriers had significantly increased risk of developing subsequent clinical C. difficile infection as compared to non-carriers (HR 23.9, 95% CI: 7.2-79.6, p<0.001, Figure 1).

Figure 1:

Kaplan-Meier Survival Curve for Time to Symptomatic C. difficile Infection for the C. difficile carriers (dashed line) and the non-carriers (solid line). There was a statistically significant difference (p<0.001). The Hazard Ratio is 23.9 (p<0.001; 95% CI 7.2 – 79.6).

Discussion

In this prospective cohort study, we found that 9.6% of subjects being admitted in a large academic medical center were asymptomatic C. difficile carriers including 10.2% of nursing facility residents and 7.7% of community residents. Among C. difficile carriers identified at enrollment, 38.1% were subsequently diagnosed with symptomatic C. difficile infection, most progressing within 2 weeks, while only 2.0% of non-carriers were subsequently diagnosed with symptomatic C. difficile infection. Only 8.5% of potential subjects declined to participate despite the sensitive nature of perirectal swabbing, suggesting that screening of asymptomatic patients is feasible.

Previous studies reveal widely varying prevalence estimates of asymptomatic C. difficile carriage in healthcare facilities. The overall raw prevalence of asymptomatic C. difficile infection in our sample (9.6%) is consistent with recent estimates of C. difficile carriage among admitted patients which vary from 0.6-13%.[25 26] In contrast, we found a lower prevalence of asymptomatic carriage among nursing facility residents (10.2%) than prior studies which have found up to 51%.[9 27-29] Our lower prevalence may reflect a different underlying population, geographic variation, and/or the success of antibiotic stewardship programs.

Although C. difficile carriers shed fewer spores than symptomatic C. difficile patients,[10 17 30 31] given their larger numbers, carriers may actually be responsible for a larger C. difficile spore burden and more transmission than symptomatic patients.[5 32] Strategies to reduce transmission from asymptomatic carriers to uninfected individuals have included preemptive modified isolation,[33] heightened cleaning of units at risk,[34 35] intensified antibiotic time outs for carriers,[36] or even prophylactic treatment for those at highest risk such as oncologic or chronically immunosuppressed patients.[37] Many of these strategies, however, require routine early identification of carriers.

In this study, the only clinical or demographic feature that was associated with carriage was swab soilage, which is visible fecal material staining the swab. We hypothesize that swab soilage represents improved testing sensitivity in the presence of frank fecal material, or instead could mean stool incontinence, poor hygiene or an inability to care for oneself effectively. Further study could elucidate the cause of this association.

The present study adds to the limited body of literature examining the rate of progression from C. difficile carriage to clinical C. difficile infection. An older review of 810 patients in 4 studies admitted to large US hospitals[8] found a lower rate of progression to symptomatic C. difficile among carriers than non-carriers, and thus it was thought that C. difficile carriage was protective against symptomatic C. difficile. Newer studies show that carriers are at higher risk for subsequent infection though in each study the timeframe in which carriers were followed was limited to 14 days,[13] during the admission,[6 15 16] or 1 month following discharge.[14] We found a higher rate of progression from carrier to symptomatic infection (38.1%) compared with only 2.0% among non-carriers when followed for up to 6 months. Due to the high rate of progression, it is possible that a substantial proportion of “healthcare facility-onset”[18] C. difficile may actually result from the progression from C. difficile carriage to symptomatic C. difficile especially within the first two weeks of hospitalization.

Several study limitations should be noted. First, given the lower than expected number of C. difficile carriers, the study had limited power to detect a difference in the proportion of nursing facility and community residents who were C. difficile carriers. Second, inquiry about the subsequent development of diarrhea was left up to the primary team, which may have led to a symptomatic C. difficile infection going unnoticed and undiagnosed, leading to an underestimate of symptomatic infection in carriers and non-carriers. Third, to screen for asymptomatic carriage we used perirectal swabbing rather than rectal swabbing or stool specimens. While perirectal swabbing may have underestimated the true prevalence of C. difficile carriers, the high frequency of soiled test swabs as well as the likely better acceptability of perirectal swabbing as a screening tool made this the preferred modality. Lastly, retrospective data on antibiotic use and prospective data on C. difficile diagnosis was limited to usage and diagnosis only within our healthcare system as recorded in the electronic medical record.

Conclusions

Asymptomatic carriers may represent a significant reservoir for transmission of C. difficile, and progression from asymptomatic carriage to symptomatic infection may account for a significant proportion of C. difficile infection that is classified as “healthcare facility-onset”. Therefore, identification of asymptomatic carriers could reduce the spread of C. difficile. Specific environmental, isolation and stewardship strategies to prevent spread of C. difficile from carriers to uninfected patients as well as prevent progression to symptomatic C. difficile infection warrant further study.