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S. aureus transmission from health care workers rare
Health care workers rarely transmitted Staphylococcus aureus to patients in an ICU where standard infection control measures were in place, according to results of a longitudinal cohort study in the U.K.
“S. aureus is transmissible between patients, particularly in high-dependency settings. Hospitals invest considerable efforts in prevention of direct patient-to-patient transmission or transmission via staff and the environment,” James R. Price, PhD, of the department of microbiology and infection at Royal Sussex County Hospital, Brighton, England, and colleagues wrote. “Colonized health care workers have been implicated as sources of transmission in outbreaks, but the use of health care worker screening and S. aureus eradication as routine control measures is controversial.
Researchers performed a 14-month study in the ICU and high-dependency unit of Royal Sussex County Hospital between Oct. 31, 2011 and Dec. 23, 2012. Price and colleagues collected nasal swabs from health care workers every 4 weeks, and from patients at the time of admission, weekly during their hospital stays and at discharge. They also obtained samples from bed spaces once a month. The researchers then sequenced the genome of each culture, using a threshold of 40 single-nucleotide variants or less to identify different subtypes and determine S. aureus transmission.
Price and colleagues took samples from 40 locations in the hospital, 198 health care workers and 1,854 patients, ultimately sequencing 1,819 isolates. Health care workers had a S. aureus nasal carriage rate of 36.9% (interquartile range, 35.7%-37.3%), researchers reported, with carriage rates distributed evenly among doctors, nurses and physiotherapists (P = .5). Seventy-three workers (37%) were nasal carriers at enrollment, eight (4%) of whom carried MRSA. Fifty-eight percent (n = 115) of workers carried S. aureus at least once during the study period.
S. aureus presence in environmental samples ranged from 8% to 50% throughout the study, and researchers identified 605 different subtypes. Although 97 patients acquired S. aureus, the researchers identified just 25 transmissions of S. aureus, including seven transmissions from health care workers to patients, 16 from other patients and two from the environment, Price and colleagues wrote.
“The high genetic diversity and low level of transmission we observed contrast strikingly with findings from studies in low-income settings with lower barriers to transmission, in which multiple transmissions of small numbers of strains have been documented,” the researchers wrote. “Our findings therefore underscore the effectiveness and importance of measures implemented to prevent nosocomial transmission.”
In an accompanying editorial, Olivier Denis, MD, PhD, of the National Reference Centre for Staphylococcus Aureus, Hopital Erasme, Brussels, wrote that the study “highlights the complexity of S. aureus dynamic in ICUs with standard infection control measures.
“These results reinforce previous findings that, in most cases, endogenous staphylococcal colonization causes subsequent infections, particularly in some groups such as patients with impaired skin barriers. Therefore, strategies based on elimination of nasal carriage represent an ineffective strategy to reduce the incidence of S. aureus infections.”
Denis noted, however, that the study was limited by its non-epidemic setting.
“Further investigations compiling epidemiological and genetic data are essential to determine the multiple sources of transmission and to assess the effectiveness of strategies for the prevention of nosocomial infections,” he wrote. – by Andy Polhamus
Disclosure: Price and Denis report no relevant disclosures. Please see the full study for a complete list of all other researchers’ relevant financial disclosures.