Bassetti, Stefano

Bischoff, Werner E.

Sherertz, Robert J.

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CORRESPONDENCE • CID 2005:40 (15 February) • 633this may have led to increased transmis-sion of multidrug-resistant nosocomialpathogens on the gloved hands of healthcare workers [5]. Another possible ex-planation for the paradoxical increase inMRSA rates during the SARS outbreakcould be the shunting of limited infec-tion-control resources to SARS case sur-veillance and epidemiology and awayfrom mainstream infection-control ac-tivities, thus compromising the effec-tiveness of baseline control measuresagainst nosocomial infections.As our data reinforce, during periods ofintense alert for novel emerging patho-gens, such as SARS coronavirus and avi-an influenza virus, it is imperative that“conventional” practices of infection con-trol not be overlooked, because they re-main essential for the control of infectionwith endemic nosocomial pathogens inour midst.AcknowledgmentsPotential conflicts of interest. All authors: noconflicts.Louis Y. A. Chai,1 Toon Mae Ng,3Abdulrazaq G. Habib,1 Kamaljit Singh,1,2Gamini Kumarasinghe,2 and Paul A. Tambyah1Departments of 1Medicine and 2Microbiologyand 3Infection Control Unit,National University Hospital, SingaporeReferences1. Yap FHY, Gomersall CD, Fung KSC, et al. In-crease in methicillin-resistant Staphylococcusaureus acquisition rate and change in patternassociated with an outbreak of severe acute re-spiratory syndrome. Clin Infect Dis 2004; 39:511–6.2. Boyce JM, Havill NL, Kohan C, et al. Do in-fection control measures work for methicillin-resistant Staphylococcus aureus? Infect ControlHosp Epidemiol 2004; 25:395–401.3. Goldman DA. The role of barrier precautions ininfection control. J Hosp Infect 1991; 18(SupplA):515–23.4. Horikawa K, Murakami K, Kawano F. Isola-tion and characterization of methicillin-resis-tant Staphylococcus aureus strains from thenares of nurses and their gowns. Microbiol Res2001; 155:345–9.5. Boyce JM, Potter-Bynoe G, Chenevert C, et al.Environmental contamination due to methi-cillin-resistant Staphylococcus aureus: possibleinfection control implications. Infect ControlHosp Epidemiol 1997; 18:622–7.6. Pittet D, Mourouga P, Perneger TV. Compli-ance with handwashing in a teaching hospital.Infection Control Programme. Ann Intern Med1999; 130:126–30.7. Pittet D, Hugonnet S, Harbarth S, et al. Effec-tiveness of a hospital-wide programme to im-prove compliance with hand hygiene. InfectionControl Programme. Lancet 2000; 356:1307–12.Reprints or correspondence: Dr. Paul Ananth Tambyah, Dept.of Medicine, National University Hospital Singapore, 5 LowerKent Ridge Rd., Singapore 119074 (mdcpat@nus.edu.sg).Clinical Infectious Diseases 2005; 40:632–3 2005 by the Infectious Diseases Society of America. Allrights reserved. 1058-4838/2005/4004-0026$15.00Outbreak of Methicillin-Resistant Staphylococcusaureus Infection Associatedwith an Outbreak of SevereAcute Respiratory SyndromeSir—We read with great interest the re-cent article by Yap et al. [1]. The au-thors report a significant increase in themethicillin-resistant Staphylococcus aureus(MRSA) acquisition rate, with a very highrate of ventilator-associated pneumonia—caused mainly by MRSA—in patients withsevere acute respiratory syndrome (SARS)in an intensive care unit (ICU) that ad-mitted only patients with SARS. Para-doxically, this increase occurred afterinfection-control measures (including thewearing of gloves and gowns at all times)were upgraded because of the SARS out-break and despite a low importation rateof MRSA into the ICU.Yap et al. [1] provide 3 possible expla-nations for this observation. First, thepractice of wearing gloves at all times mayhave led to poor compliance with handhygiene, and the routine wearing of long-sleeved gowns, which were not changedbetween contact with patients, could alsohave contributed to cross-transmission ofMRSA. Second, the heavy use of anti-microbials active against gram-negativeorganisms could have promoted the ov-ergrowth of MRSA. Third, the SARS-associated coronavirus (SARS-CoV) maypredispose patients to secondary infectionwith S. aureus.We agree with these hypotheses, but wedisagree with the conclusion that “cross-transmission of MRSA may be increased… if the [infection-control] measures in-cluded excessive use of gloves and gowns”[1, p. 515]. An alternative explanation forthe significant increase in the rate ofMRSA acquisition may be a viral-bacterialinteraction between SARS-CoV and S. au-reus, leading to an explosive airborne dis-persal of S. aureus and a very efficienttransmission of MRSA from colonized tononcolonized patients (the “cloud phe-nomenon”). This phenomenon was de-scribed by Eichenwald et al. [2], whoshowed that newborn infants who are na-sally colonized with S. aureus produce sig-nificant airborne S. aureus dispersal andbecome highly contagious after infectionwith a respiratory virus. These babiescaused explosive outbreaks of S. aureusinfection in nurseries. Because they wereliterally surrounded by clouds of bacteria,they were called “cloud babies” [2]. Wehave recently shown that the same mech-anism also occurs in certain adult nasalS. aureus carriers (“cloud adults”) [3–5].Reports in the literature describe singlehealth care workers nasally colonized withS. aureus who originated nosocomial S. au-reus epidemics while experiencing a viralinfection of the upper respiratory tract. Thisconfirms that “cloud adults” can cause out-breaks [3, 6, 7]. Our data also indicate thatclothing contaminated with S. aureus canamplify the dispersal of these bacteria intothe air [4, 5], in agreement with previousobservations [8, 9].In conclusion, aerial dissemination ofMRSA because of the “cloud phenome-non” may be the main reason for the de-scribed epidemic of MRSA infection. Thismay have occurred as a result of directaerial dissemination or as a result of heavycontamination of the environment of col-onized patients (including contaminationof patient bedclothes or health care workergowns). This, in combination with diffi-culties associated with frequently changinggloves and gowns, may have greatly facil-itated MRSA cross-infection during theSARS outbreak.634 • CID 2005:40 (15 February) • CORRESPONDENCEAcknowledgmentsPotential conflicts of interest. All authors: noconflicts.Stefano Bassetti,1 Werner E. Bischoff,2and Robert J. Sherertz21Division of Infectious Diseases, University HospitalBasel, Basel, Switzerland; and 2Sectionon Infectious Disease, Wake Forest UniversitySchool of Medicine, Winston-Salem,North CarolinaReferences1. Yap FH, Gomersall, CD, Fung KS, et al. Increasein methicillin-resistant Staphylococcus aureusacqusition rate and change in pathogen pat-tern associated with an outbreak of severeacute respiratory syndrome. Clin Infect Dis2004; 39:511–6.2. Eichenwald HF, Kotsevalov O, Fasso LA. The“cloud baby”: an example of bacterial-viral in-teraction. Am J Dis Child 1960; 100:161–73.3. Sherertz RJ, Reagan DR, Hampton KD, et al.A cloud adult: the Staphylococcus aureus–virusinteraction revisited. Ann Intern Med 1996;124:539–47.4. Bassetti S, Bischoff WE, Walter M, et al. Dis-persal of Staphylococcus aureus into the air as-sociated with a rhinovirus infection. InfectControl Hosp Epidemiol (in press).5. Bischoff WE, Bassetti S, Bassetti-Wyss BA, etal. Airborne dispersal as a novel transmissionroute of coagulase-negative staphylococci: in-teraction between coagulase-negative staphy-lococci and rhinovirus infection. Infect ControlHosp Epidemiol 2004; 25:504–11.6. Belani A, Sherertz RJ, Sullivan ML, Russell BA,Reumen PD. Outbreak of staphylococcal infec-tion in two hospital nurseries traced to a singlenasal carrier. Infect Control 1986; 7:487–90.7. Sherertz RJ, Bassetti S, Bassetti-Wyss B.“Cloud” health-care workers. Emerg Infect Dis2001; 7:241–4.8. Duguid JP, Wallace AT. Air infection with dustliberated from clothing. Lancet 1948; 2:845–9.9. Hare R, Thomas CG. The transmission ofStaphylococcus aureus. Brit Med J 1956; 2:840–4.Reprints or correspondence: Dr. Stefano Bassetti, Div. of In-fectious Diseases, University Hospital Basel, Petersgraben 4,CH-4031 Basel, Switzerland (sbassetti@uhbs.ch).Clinical Infectious Diseases 2005; 40:633–4 2005 by the Infectious Diseases Society of America. Allrights reserved. 1058-4838/2005/4004-0027$15.00Reply to Bassetti et al.Sir—We appreciate the comments on ourarticle [1] by Bassetti et al. [2]. We agreethat the fourth hypothesis, relating to the“cloud” phenomenon [3–5], may contrib-ute to the spread of methicillin-resistantStaphylococcus aureus (MRSA).However, we do not think that thecloud phenomenon is the main reason forthe MRSA epidemic we describe [1]. Dur-ing the study period, all staff in the inten-sive care unit (ICU) wore N95 masks. Be-cause masks are effective in reducing thedispersal of MRSA [5], “cloud” health careworkers would be an unlikely explanationfor the epidemic. For patients who carryS. aureus in the nares, it appears that ac-tive breathing, sneezing, nose blowing, orsnorting to the open air are importantin the formation of airborne bacterial“clouds.” We would like to point out thatit is unlikely that our patients performedthese activities to a significant extent. Un-like in patients with rhinovirus infection,nasal symptoms are rare in patients withsevere acute respiratory syndrome. Fur-thermore, precautions to control aerosolspread in the ICU were extremely strictduring the period of the SARS outbreak.The majority of patients received me-chanical ventilation. All circuit connectionand disconnection procedures were per-formed with extreme caution, and all suc-tioning was conducted in closed-suctionsystems. A high-efficiency bacterial/viralfilter was incorporated into each breathingcircuit, and the exhalation port of the ven-tilator was connected to scavenging sys-tems. Surgical masks were worn by spon-taneously breathing patients with nasalcannula or oxygen masks. For patientsrequiring high-flow oxygen, tight-fittingmasks with filters were used. Use of Ven-turi-type masks, nebulization, and non-invasive positive-pressure ventilation wereall avoided. Therefore, “explosive” disper-sal of droplets or aerosols would have beenunlikely.During the outbreak of SARS, there wasa hospital (Queen Mary Hospital; Pok-fulam, Hong Kong) that explicitly banned“gloving all the time” and instead pro-moted glove use “only when indicated”and meticulous hand washing. This hos-pital managed a total of 52 cases of SARS,which is a substantially lower number ofcases than were treated at our institution(Prince of Wales Hospital, Hong Kong).There was no change in the rate of MRSAacquisition in the ICU or in the hospi-tal in general (W. H. Seto, personalcommunication).In a health care environment, patientcontact is the main mode of transmissionfor MRSA. During the period we reported,gloves were worn at all times by healthcare workers, and hands were not neces-sarily always washed between the chang-ing of gloves [1]. These practices—to-gether with the excessive use of antibiotics,including fluoroquinolones—may be themain driving factors underlying the out-break of MRSA infection. After removalof gloves, hands are commonly contami-nated with nosocomial pathogens such asMRSA, with contamination rates of up to50% [6]. Occult breaks in latex gloves cancause substantial contamination of thehands [7], and it has been reported that20% of latex gloves that had passed thewatertight test allowed penetration of bac-teria to the hands [8].The “cloud” phenomenon is an in-teresting subject, and its relevance in thenosocomial transmission of pathogens de-serves further evaluation. Health care work-ers should understand that wearing ofgloves is not a substitute for hand washing.AcknowledgmentsPotential conflicts of interest. All authors: noconflicts.Florence H. Y. Yap,1 Pak-Leung Ho,2and Gavin M. Joynt11Department of Anaesthesia and Intensive Care,Prince of Wales Hospital, Chinese Universityof Hong Kong, and 2Department of Microbiologyand Centre of Infection, Queen Mary Hospital,University of Hong Kong, Hong KongSpecial Administrative RegionReferences1. Yap FH, Gomersall CD, Fung KS, et al. Increasein methicillin-resistant Staphylococcus aureusacquisition rate and change in pathogen patternassociated with an outbreak of acute severe re-spiratory syndrome. Clin Infect Dis 2004; 39:511–6.

Outbreak of Methicillin-Resistant Staphylococcus aureus Infection Associated with an Outbreak of Severe Acute Respiratory Syndrome

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