Route of transmission of Staphylococcus aureu s
Authors: Olivier Denis
Journal: The Lancet Infectious Diseases (2016)

Health-care-associated infections represent a major health concern with a substantial impact on morbidity and mortality. The prevalence of nosocomial infections is especially high in intensive care units (ICUs), where the occurrence of multidrug-resistant pathogens is highest in the hospital.1Vincent JL Rello J Marshall J et al.International study of the prevalence and outcomes of infection in intensive care units.JAMA. 2009; 302: 2323-2329Crossref PubMed Scopus (2327) Google Scholar Staphylococcus aureus is a major agent of health-care-associated infections that causes a wide range of diseases from mild to life-threatening conditions. It is one of the most prevalent causes of nosocomial bacteraemia, hospital-acquired pneumonia, and surgical site infections.1Vincent JL Rello J Marshall J et al.International study of the prevalence and outcomes of infection in intensive care units.JAMA. 2009; 302: 2323-2329Crossref PubMed Scopus (2327) Google Scholar, 2Weiner LM Webb AK Limbago B et al.Antimicrobial-resistant pathogens associated with healthcare-associated infections: summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2011–2014.Infect Control Hosp Epidemiol. 2016; 37: 1288-1301Crossref PubMed Scopus (717) Google Scholar Additionally, this bacterium has a high potential to acquire antimicrobial resistance. After its first report in 1961, meticillin-resistant S aureus (MRSA) has subsequently spread worldwide, causing major outbreaks in acute and chronic care facilities. Data from the European Antimicrobial Resistance Surveillance System3de Kraker ME Jarlier V Monen JC Heuer OE van de Sande N Grundmann H The changing epidemiology of bacteraemias in Europe: trends from the European Antimicrobial Resistance Surveillance System.Clin Microbiol Infect. 2013; 19: 860-868Summary Full Text Full Text PDF PubMed Scopus (262) Google Scholar suggest that the frequency of MRSA bacteraemia is slowly decreasing in the past 10 years in Europe, but this trend was clearly counterbalanced by the increasing burden of bloodstream infections caused by meticillin-susceptible S aureus (MSSA). The squamous epithelium of the anterior nares is the primary natural reservoir of S aureus in human beings.4Mulcahy ME McLoughlin RM Host–bacterial crosstalk determines Staphylococcus aureus nasal colonization.Trends Microbiol. 2016; 24: 872-886Summary Full Text Full Text PDF PubMed Scopus (66) Google Scholar Historically, three patterns of colonisation have been described—persistent carriers (roughly 20% of the general population), intermittent carriers (30%), and non-carriers (50%). In 2009, van Belkum and colleagues5Van Belkum A Verkaik NJ de Vogel CP et al.Reclassification of Staphylococcus aureus nasal carriage types.J Infect Dis. 2009; 199: 1820-1826Crossref PubMed Scopus (295) Google Scholar proposed the redefinition of S aureus nasal carriage types as persistent and "other" on the basis of anti-staphylococcal antibody profiles, since intermittent carriers and non-carriers share similar S aureus nasal elimination kinetics. Persistent carriers have a higher density of S aureus in the nose than intermittent carriers and usually harbour a single genotype.4Mulcahy ME McLoughlin RM Host–bacterial crosstalk determines Staphylococcus aureus nasal colonization.Trends Microbiol. 2016; 24: 872-886Summary Full Text Full Text PDF PubMed Scopus (66) Google Scholar Importantly, persistent nasal carriage of S aureus is strongly associated with an increased risk for development of nosocomial infections such as bacteraemia, dialysis infections, and surgical site infections.6Simor AE Staphylococcal decolonisation: an effective strategy for prevention of infection?.Lancet Infect Dis. 2011; 11: 952-962Summary Full Text Full Text PDF PubMed Scopus (75) Google Scholar Therefore, endogenous contamination of S aureus is considered to have a major role in the pathogenesis of staphylococcal infections. Possible route for transmission of S aureus includes other patients, health-care workers, and the ICU environment. In The Lancet Infectious Diseases, James R Price and colleagues7Price JR Cole K Bexley A et al.Transmission of Staphylococcus aureus between health-care workers, the environment, and patient in an intensive care unit: a longitudinal cohort study based on whole-genome sequencing.Lancet Infect Dis. 2016; (published online Nov 15.)http://dx.doi.org/10.1016/S1473-3099(16)30413-3Google Scholar report results of their longitudinal cohort study, in which they used whole-genome sequencing to analyse 1819 S aureus isolates collected in an adult ICU and high-dependency unit (HDU).7Price JR Cole K Bexley A et al.Transmission of Staphylococcus aureus between health-care workers, the environment, and patient in an intensive care unit: a longitudinal cohort study based on whole-genome sequencing.Lancet Infect Dis. 2016; (published online Nov 15.)http://dx.doi.org/10.1016/S1473-3099(16)30413-3Google Scholar In the 14 month study period, 1854 patients were sampled for S aureus culture at admission to the ICU or HDU, weekly thereafter, and at discharge. In parallel, 198 health-care workers and 40 near-patient environmental locations were screened at 4 week intervals. The active surveillance identified 386 (21%) of 1854 patients with nasal staphylococcal carriage at admission and 115 (58%) of 198 health-care workers who yielded positive culture for S aureus, including 36 (19%) who were persistent carriers. Whole-genome sequencing results showed that most isolates had high genetic diversity. Notably, of 97 patient acquisitions of S aureus observed during the study, only 25 transmissions (ie, with pairs of isolates differing by no more than 40 single-nucleotide variants)—seven from health-care workers, two from the environment, and 16 from other patients—were identified . The study had some limitations. First, data for some important risk factors for S aureus acquisition—including antibiotic use, hand hygiene compliance, and S aureus colonisation pressure over time—were not available.8Bloemendaal AL Fluit AC Jansen WM et al.Acquisition and cross-transmission of Staphylococcus aureus in European intensive care units.Infect Control Hosp Epidemiol. 2009; 30: 117-124Crossref PubMed Scopus (51) Google Scholar Second, the 4 week interval between screening of health-care workers could underestimate the role of transient carriage in transmission of S aureus from health-care workers to patients. Nevertheless, this study highlights the complexity of S aureus dynamic in ICUs with standard infection control measures. The authors showed the limited role of the environment and health-care workers in transmission of S aureus to patients. These results reinforce previous findings that, in most cases, endogenous staphylococcal colonisation causes subsequent infections, particularly in some groups such as patients with impaired skin barriers.9Kalmeijer MD Coertjens H van Nieuwland-Bollen PM et al.Surgical site infections in orthopedic surgery: the effect of mupirocin nasal ointment in a double-blind, randomized, placebo-controlled study.Clin Infect Dis. 2002; 35: 353-358Crossref PubMed Scopus (267) Google Scholar, 10Von Eiff C Beker K Machka K Stammer H Peters G Nasal carriage as a source of Staphylococcus aureus bacteremia.N Engl J Med. 2001; 344: 11-16Crossref PubMed Scopus (1503) Google Scholar Therefore, strategies based on elimination of nasal carriage represent an effective strategy to reduce the incidence of S aureus infections.6Simor AE Staphylococcal decolonisation: an effective strategy for prevention of infection?.Lancet Infect Dis. 2011; 11: 952-962Summary Full Text Full Text PDF PubMed Scopus (75) Google Scholar, 9Kalmeijer MD Coertjens H van Nieuwland-Bollen PM et al.Surgical site infections in orthopedic surgery: the effect of mupirocin nasal ointment in a double-blind, randomized, placebo-controlled study.Clin Infect Dis. 2002; 35: 353-358Crossref PubMed Scopus (267) Google Scholar However, we should keep in mind that Price and colleagues' study was done in a non-epidemic context with a low prevalence of MRSA. The use of whole-genome sequencing, with its high discriminatory power, will allow us to better understand the different route of transmission of important human pathogens such as S aureus.11Köser CU Holden MT Ellington MJ et al.Rapid whole-genome sequencing for investigation of a neonatal MRSA outbreak.N Engl J Med. 2012; 366: 2267-2275Crossref PubMed Scopus (487) Google Scholar, 12Roisin S Gaudin C De Mendonça R et al.Pan-genome multilocus sequence typing and outbreak-specific reference-based single nucleotide polymorphism analysis to resolve two concurrent Staphylococcus aureus outbreaks in neonatal services.Clin Microbiol Infect. 2016; 22: 520-526Summary Full Text Full Text PDF PubMed Scopus (22) Google Scholar Further investigations compiling epidemiological and genetic data are essential to determine the multiple sources of transmission and to assess the effectiveness of strategies for prevention of nosocomial infections. I declare no competing interests. Transmission of Staphylococcus aureus between health-care workers, the environment, and patients in an intensive care unit: a longitudinal cohort study based on whole-genome sequencingIn the presence of standard infection control measures, health-care workers were infrequently sources of transmission to patients. S aureus epidemiology in the ICU and HDU is characterised by continuous ingress of distinct subtypes rather than transmission of genetically related strains. Full-Text PDF Open AccessStaphylococcus aureus in critical careThe Article by James Price and colleagues1 describes an important study that explores the role of health-care workers and the environment in patient acquisition of Staphylococcus aureus. We congratulate the team on the study, which, impressively, enrolled 95% of eligible health-care workers who, along with patients and the environment, were screened for S aureus; the large number of isolates were then analysed using whole-genome sequencing. Full-Text PDF