Is environmental contamination associated with Staphylococcus aureus clinical infection in maximum security prisons

Over the past decade, large outbreaks of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have occurred in correctional facilities across the country.1,2 Although many have been managed with aggressive interventions, response to standard infection control procedures has been variable, highlighting our incomplete understanding of staphylococcal transmission in this setting.2 Environmental contamination has recently emerged as a possible target for novel prevention and control strategies.3,4 This study sought to characterize the relationship between environmental contamination and clinical infection in this vulnerable population. We conducted a case-control study of S. aureus environmental contamination at 2 New York State (NYS) maximum security prisons: Sing Sing (men) and Bedford Hills (women). Prisoners with documented S. aureus skin infections were identified by medical personnel at each prison. For every case, 2 uninfected controls—1 nasally and/or oropharyngeally colonized with S. aureus and 1 noncolonized—were selected from the same prison in a contemporaneous fashion. These were identified through our research group’s ongoing study of S. aureus colonization in NYS prisons.5 Consenting study participants had a standardized set of environmental surfaces cultured within 1 week of infection diagnosis (cases) or selection (controls). These included bed sheets, sink handles, toilet flushes, toilet seats, cell bars, light switches, soap dishes, window handles, locker handles, and radios but varied on the basis of the prisoner’s cell contents. Cultures were also obtained from shared gymnasiums in each prison at study initiation. All samples were collected using premoistened rayon-tipped swabs and qualitatively cultured as described else-where.5 S. aureus isolates were typed by polymerase chain reaction sequencing of the spa (staphylococcal protein A) gene.6 SAS (ver. 9.2; SAS Institute) was utilized for data analysis. The study was approved by the Columbia University and NYS Department of Corrections Institutional Review Boards. Ten cases were enrolled in this study. Twenty controls were selected, but 2 did not meet inclusion criteria. There were no significant associations between case status and the demographic and exposure variables assessed (sex, age, race/ ethnicity, self-perceived health, shower frequency, and gym use). The proportion of subjects with S. aureus contamination on 1 or more surfaces did not vary appreciably on the basis of infection status (3/10 cases [30%] vs 6/18 controls overall [33.3%]; Table 1). Despite this, environmental contamination of controls varied depending on their colonization status. Surface contamination, when present, was more frequent among cases than among controls (13/18 surfaces from 3 cases [72.2%] vs 20/43 surfaces from 6 controls [46.5%]; P = .07). Six clonal types were identified on surfaces of the 9 contaminated cells; only 1 cell had more than 1 clone present. None of the infectious, colonization, or personal environmental isolates were methicillin resistant. TABLE 1 Environmental Contamination of Cases and Controls Of the 20 items sampled in the Sing Sing gymnasium, 8 (40%) were positive for S. aureus. These included the gym door handle, boxing gloves, basketballs, abdominal crunch machine, seated and upright leg presses, and hand sanitizer dispenser. Among these surfaces, 6 clonal types were found (spa t002, t008, t334, t701, t1510, and t2334), and all were methicillin susceptible. The Bedford Hills gymnasium was not heavily contaminated; 2 (7.7%) of 26 surfaces were positive, 1 with methicillin-resistant spa t008. Few studies have assessed the prevalence and significance of bacterial surface contamination in jails or prisons. In 2009, Felkner et al7 cultured 132 surfaces from a Texas jail in a nonoutbreak setting. S. aureus was recovered from 10 surfaces (7.6%), with the majority of isolates (8/10) resistant to methicillin. A subset of isolates (6/10) underwent pulsed-field gel electrophoresis, and two-thirds were found to be identical to the USA300 epidemic strain (spa t008). Inmates at Sing Sing and Bedford Hills are known to have high rates of asymptomatic colonization with MRSA (11.2% and 11.1%, respectively) and USA300 (10% and 12.4%, respectively).5 Although this study documented a high prevalence of staphylococcal contamination, only 1 (0.4%) of the 283 environmental cultures was positive for MRSA. The etiology of this discrepancy is unclear. As previous studies have shown effective survival of USA300 and MRSA in the environment,6, 8 the comparatively low prevalence of surface contamination with these clones may be related to infection control strategies within the prison. Since USA300 is a common cause of skin abscesses, systemic antibiotics administered to those with active infection may reduce asymptomatic carriage and subsequent environmental contamination with this clone. Similarly, aggressive environmental hygiene may be differentially applied to locations highly contaminated with this strain if they are associated with purulent skin infections. Prisoners are responsible for disinfecting their own environments using quaternary ammonium products on a weekly basis. Despite this, the true frequency and intensity of cleaning may vary on the basis of prisoner preferences. Our finding of increased environmental contamination among colonized controls compared with that among noncolonized controls suggests that asymptomatic nasal and/or oropharyngeal carriage correlates with environmental reservoirs. Although every effort was made to culture cases’ cells immediately after an infection was identified, antimicrobials and disinfection administered immediately after ascertainment may have limited our ability to capture environmental contamination. Our study is further impaired by its small sample size, limited largely by a low incidence of infections over our study period. It is possible that investigations of environmental contamination during prison-based outbreaks could yield different results. Prospective studies with larger enrollments may be more effective in demonstrating small but significant trends in environmental colonization. While mounting evidence suggests a linkage between S. aureus surface contamination and clinical infection, data remain conflicting.3,4,6 Further research into prison-based infectious reservoirs will be essential to effectively protect this important population and the communities in which they reside.