A CLOUD ADULT - THE STAPHYLOCOCCUS-AUREUS - VIRUS INTERACTION REVISITED

Background: Nasal carriage of Staphylococcus aureus is common among he alth care workers, but outbreaks caused by such carriers are relativel y uncommon. We previously reported outbreaks of S. aureus skin infecti ons that affected newborn infants and were attributed to an S. aureus nasa I carrier who had had an associated upper respiratory tract infec tion (URI) during the outbreak period. Objective: To investigate the c ontribution of a nasal methicillin-resistant S. aureus (MRSA) carrier (physician 4) who contracted a URI to an outbreak of MRSA infections t hat involved 8 of 43 patients in a surgical intensive care unit during a 3-week period. Design: An epidemiologic study of an outbreak of MRS A infections and a quantitative investigation of airborne dispersal of S. aureus associated with an experimentally induced rhinoviral Infect ion. Setting: A university hospital. Participants: 43 patients in a su rgical intensive care unit and 1 physician. Measurements: Molecular ty ping was done, and risk factors for MRSA colonization were analyzed. A gar settle plates and volumetric air cultures were used to evaluate th e airborne dispersal of S. aureus by physician 4 before and after a rh inoviral infection and with or without a surgical mask. Results: A sea rch for nasal carriers of MRSA identified a single physician (physicia n 4); molecular typing showed that the MRSA strain from physician 4 an d those from the patients were identical. Multivariate logistic regres sion analysis identified exposure to physician 4 and duration of venti lation as independent risk factors for colonization with MRSA (P less than or equal to 0.008). Air cultures showed that physician 4 disperse d little S. aureus in the absence of a URI. After experimental inducti on of a rhinovirus URI, physician 4's airborne dispersal of S. aureus without a surgical mask increased 40-fold; dispersal was significantly reduced when physician 4 wore a mask (P less than or equal to 0.015). Conclusions: Physician 4 became a ''cloud adult,'' analogous to the ' 'cloud babies'' described by Eichenwald and coworkers who shed S. aure us into the air in association with viral URIs. Airborne dispersal of S. aureus in association with a URI may be an important mechanism of t ransmission of S. aureus.