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. 2004 Dec 14;24(1):65–67. doi: 10.1007/s10096-004-1256-8

Similar environmental survival patterns of Streptococcus pyogenes strains of different epidemiologic backgrounds and clinical severity

J H T Wagenvoort 1,, R J R Penders 1, B I Davies 1, R Lütticken 2
PMCID: PMC7087737  PMID: 15599644

The spectrum of Streptococcus pyogenes (group A streptococci) infections and complications includes asymptomatic carriage, throat infection, and acute rheumatic fever, localized skin, soft tissue or bone infections, and invasive spread with positive blood cultures accompanied by toxic shock leading to rapid death [15]. The contagiousness of these S. pyogenes infections has been studied extensively [13] and the contribution of environmental sources has been considered [1, 5]. Following a nosocomial outbreak at our hospital due to an S. pyogenes strain [4] in which some findings paralleled those from earlier MRSA outbreaks [6], we decided to examine the survival of S. pyogenes strains in the environment to ascertain whether extended environmental survival contributes to the organism’s spread, as noted for a number of MRSA outbreak strains at our hospital [7]. Thus, several S. pyogenes strains of different epidemiological backgrounds and clinical severity were selected, and the survival behavior of each was evaluated.

All of the S. pyogenes strains studied were diagnosed at the Atrium Medical Centre (AMC) and the German National Reference Laboratory for Streptococci at the Department of Medical Microbiology at the Rheinisch-Westfälische Technische Hochschule (RWTH) in Aachen, Germany. They were all obtained from clinical cases, and the cases reflected a wide spectrum of clinical severity or epidemiological behavior. The strains were divided into two groups and four patient subgroups: group A included strains from serious invasive infections (i.e., bacteremia, sepsis, including the manifestation of toxic shock syndrome), with subgroup 1 (strains 1 and 2) being nosocomial and subgroup 2 (strains 3 and 4) non-nosocomial; group B included strains from less serious non-invasive soft tissue or wound infections, with subgroup 3 (strains 5 and 6) being nosocomial and subgroup 4 (strains 7 and 8) non-nosocomial. S. pyogenes strains 2, 6 and 8 were isolated from different patients during a hospital outbreak reported previously by Davies et al. [4]. In Table 1 of that report the respective patients were assigned the codes G, P1 and M1.

Table 1.

Environmental survival (cfu) of Streptococcus pyogenes strains isolated from cases of varying clinical severity with a nosocomial (subgroups 1 and 3) or non-nosocomial (subgroups 2 and 4) epidemiology

Strain characteristic Group A (virulent strains) Group B (non-virulent strains)
Subgroup 1 Subgroup 2 Subgroup 3 Subgroup 4
Strain 1 Strain 2 Strain 3 Strain 4 Strain 5 Strain 6 Strain 7 Strain 8
Type M1, T1, speA M9, TB3264 M12, T12, speC M3, T3, speA M28, T28, speA, speC MNT, T25 M22–60, T12, speA, speC M28, T28
Anatomic origin Blood Blood Blood Blood Soft tissue Wound Soft tissue Wound
Nosocomial Yes Yes No No Yes Yes No No
Day of measurement
1 108 108 108 108 108 108 108 108
14 350 4000 9000 4200 4000 700 20 4000
15 190 3500 3300 2980 3000 590 10 3100
16 180 2500 2200 2910 2100 120 10 2100
17 20 2200 180 490 2000 110 10 3000
18 0 330 0 710 320 20 10 280
19 20 380 0 650 170 60 20 140
20 0 410 20 460 530 320 0 860
21 40 210 60 860 920 40 10 240
22 140 620 80 800 660 40 0 750
23 90 0 50 780 980 130 0 80
24 20 140 60 590 280 120 0 430
25 0 0 10 120 10 40 10 170
26 0 0 0 140 10 20 0 180
27 80 0 90 190 20 10 0 110
28 70 0 0 0 10 0 10 70
30 0 0 20 0 0 0 0 30
33 0 0 0 0 0 0 0 0
35 0 0 0 0 0 0 0 0
37 0 0 0 0 0 0 0 0

The influence of desiccation on the survival of the different S. pyogenes strains was evaluated and compared as described previously in detail for MRSA [7]. Suspensions containing approximately 108 cfu/ml were prepared in sterile phosphate-buffered saline (PBS; pH7.2). Samples (1 ml) of each suspension were transferred to 50-ml flat-bottomed glass bottles and allowed to dry. All bottles were plugged with cotton wool to allow free communication with the hospital environment through indirect northern light, ambient temperature and relative humidity. The fluid component of the suspensions had completely evaporated after 10 days, and sampling was begun 4 days later. Remaining viable bacteria were recovered by adding 1 ml of PBS to the bottle. After vigorous vortexing in the closed bottle, the suspension was flooded onto a blood agar plate and incubated for 48 h at 37°C. For all strains, remaining colony forming units were measured at 1–2-day intervals until extinction. The average relative humidity of the ambient air and temperature during the study period were 31% and 23°C, respectively.

The survival rates of the different groups of S. pyogenes strains are shown in Table 1. It can be seen that from an initial measurement of approximately 108 cfu the strains died off rapidly, with the decline ranging from 4 to 7-log10 cfu during the 14-day dry-out period to counts between 20 and 9,000 cfu. After day 14, only 2 more weeks passed until the last viable S. pyogenes strain was extinct. A gradual die-off pattern was noted for all strains within a range of up to circa 2-log10 cfu at the same measurement points. The last day on which a viable count was measured for each strain was between day 24 and day 30. The nosocomial outbreak strains of subgroups 1 and 3 did not survive any longer than the non-outbreak strains in subgroups 2 and 4. There was also no difference in the survival patterns exhibited by the virulent (group A) strains causing serious invasive infections (subgroups 1 and 2) and those of the less serious non-invasive (group B) strains (subgroups 3 and 4). In our approach the outcome was simple: no S. pyogenes isolate survived on glass for longer than 1 month.

The rapid decline of all S. pyogenes strains tested—even our own outbreak strain that had demonstrated MRSA-like spread [4]—contrasts sharply with the prolonged survival of around a year reported previously for epidemic MRSA strains [7]. We did not find any survival characteristics that could clearly be correlated with a specific outbreak character. S. pyogenes strains thus seem to be disseminated in a fashion similar to S. aureus, with airborne spread playing a predominant role, supported by (intermediate) carriers via dispersal on skin scales from a carriage site or via direct transmission from hands or inanimate objects. Environmental contamination was noted particularly in the outbreak related to strain no. 5, and MRSA-like spread was noted in the outbreak related to strain no. 2. The severity of disease caused by the various infecting strains did not correlate with any alternative or specific survival pattern.

The potential danger of a contaminated environment has been recognized in earlier outbreaks [1, 5], and control measures aimed at removing dust and disinfecting surfaces were consequently implemented at our hospital during the outbreaks. Although the 4-week survival period found for our S. pyogenes strains in the hospital environment is shorter than the period of 3 months reported by Lidwell and Lowbury [8], it should be noted that their study measured survival in dust. Since the influence of various dust mixtures can be surprisingly variable [7], we chose not to include dust samples in our investigational approach.

Our finding that S. pyogenes strains survive in the inanimate environment for up to 1 month shows that contact transmission is facilitated in the short-term phase of an outbreak; however, long-term environmental survival cannot be considered an important factor in the dynamics of S. pyogenes transmission. The remarkable paucity of reports on the environmental survival of S. pyogenes strains could be related to the increasing interest in the behavior of other bacteria in the hospital environment, such as multiresistant pathogens, like MRSA [7, 9], vancomycin-resistant enterococci, Clostridium difficile or Acinetobacter baumannii [9], and the coronavirus causing severe acute respiratory syndrome. Investigation of the last syndrome has identified the survival of the pathogen in fomites as a factor possibly related to transmission [10]; thus, multiple pathways must be considered for transmission of all pathogens, including S. pyogenes.

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