Surgical Mask vs N95 Respirator for Preventing
                                          Influenza Among Health Care Worke...
ORIGINAL CONTRIBUTION                                                                                                     ...

in nonexperimental settings is not well          Nurses expecte...

any of 1 of the following symptoms or            Secondary outc...

were based on consensus by clinician                           ...

4-fold or greater rise in serum titers to     31 (70.5%) in the...

tion among participants. There were no        the N95 respirato...

have biased the study toward noninfe-                      REFE...
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Mascarillas quirurgicas, N95 e influenza

  1. 1. Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers: A Randomized Trial Online article and related content current as of August 3, 2010. Mark Loeb; Nancy Dafoe; James Mahony; et al. JAMA. 2009;302(17):1865-1871 (doi:10.1001/jama.2009.1466) Correction Contact me if this article is corrected. Citations This article has been cited 19 times. Contact me when this article is cited. Topic collections Viral Infections; Occupational and Environmental Medicine; Randomized Controlled Trial; H1N1 Influenza; Infectious Diseases Contact me when new articles are published in these topic areas. Related Articles published in Respiratory Protection Against Influenza the same issue Arjun Srinivasan et al. JAMA. 2009;302(17):1903. Related Letters Surgical Masks vs N95 Respirators for Preventing Influenza Ted E. Palen et al. JAMA. 2010;303(10):937. Roger Bitar. JAMA. 2010;303(10):937. Neville Clynes. JAMA. 2010;303(10):937. Yaron Finkelstein et al. JAMA. 2010;303(10):938. Subscribe Email Alerts Permissions Reprints/E-prints Downloaded from at unknown institution on August 3, 2010
  2. 2. ORIGINAL CONTRIBUTION JAMA-EXPRESS Surgical Mask vs N95 Respirator for Preventing Influenza Among Health Care Workers A Randomized Trial Mark Loeb, MD, MSc Context Data about the effectiveness of the surgical mask compared with the N95 Nancy Dafoe, RN respirator for protecting health care workers against influenza are sparse. Given the James Mahony, PhD likelihood that N95 respirators will be in short supply during a pandemic and not avail- able in many countries, knowing the effectiveness of the surgical mask is of public Michael John, MD health importance. Alicia Sarabia, MD Objective To compare the surgical mask with the N95 respirator in protecting health Verne Glavin, MD care workers against influenza. Richard Webby, PhD Design, Setting, and Participants Noninferiority randomized controlled trial of 446 nurses in emergency departments, medical units, and pediatric units in 8 tertiary Marek Smieja, MD care Ontario hospitals. David J. D. Earn, PhD Intervention Assignment to either a fit-tested N95 respirator or a surgical mask when Sylvia Chong, BSc providing care to patients with febrile respiratory illness during the 2008-2009 influ- enza season. Ashley Webb, BS Main Outcome Measures The primary outcome was laboratory-confirmed influ- Stephen D. Walter, PhD enza measured by polymerase chain reaction or a 4-fold rise in hemagglutinin titers. I NFLUENZA CAUSES ANNUAL EPIDEM- Effectiveness of the surgical mask was assessed as noninferiority of the surgical mask ics of respiratory illness worldwide compared with the N95 respirator. The criterion for noninferiority was met if the lower and is the most important cause of limit of the 95% confidence interval (CI) for the reduction in incidence (N95 respira- tor minus surgical group) was greater than −9%. medically attended acute respira- tory illness.1,2 Moreover, there is increas- Results Between September 23, 2008, and December 8, 2008, 478 nurses were as- ing concern about the recently de- sessed for eligibility and 446 nurses were enrolled and randomly assigned the interven- tion; 225 were allocated to receive surgical masks and 221 to N95 respirators. Influenza clared influenza pandemic due to 2009 infection occurred in 50 nurses (23.6%) in the surgical mask group and in 48 (22.9%) influenza A(H1N1) in humans.3-5 in the N95 respirator group (absolute risk difference, −0.73%; 95% CI, −8.8% to 7.3%; Transmission of influenza can oc- P=.86), the lower confidence limit being inside the noninferiority limit of −9%. cur by coughing or sneezing where in- Conclusion Among nurses in Ontario tertiary care hospitals, use of a surgical mask fectious particles of variable size, rang- compared with an N95 respirator resulted in noninferior rates of laboratory- ing from approximately 0.1 to 100 µm, confirmed influenza. may be inhaled.6 This range of par- Trial Registration Identifier: NCT00756574 ticles has a yet undefined but possibly JAMA. 2009;302(17):1865-1871 important role in transmission. Al- though data from animal models and Author Affiliations: Departments of Pathology and of Western Ontario, London (Dr John); Department human experimental studies suggest Molecular Medicine (Drs Loeb, Mahony, and Smieja of Microbiology, Credit Valley Hospital, Mississauga, that short-range inhalational transmis- and Ms Dafoe), Medicine (Dr Loeb), Clinical Epide- Ontario (Dr Sarabia); Joseph Brant Memorial Hospi- sion with small droplet nuclei ( 10 miology and Biostatistics (Drs Loeb, Smieja, Earn, and tal, Burlington, Ontario (Dr Glavin); and World Health Walter), and Mathematics and Statistics (Dr Earn), Organization Collaborating Center for Studies on the µm) can occur,7-11 the exact nature of Michael G. DeGroote Institute for Infectious Disease Ecology of Influenza in Animals and Birds, St Judes Chil- transmission of influenza that occurs Research (Drs Loeb, Mahony, Smieja, and Earn), dren’s Hospital, Memphis, Tennessee (Dr Webby and McMaster University, Hamilton, Ontario, Canada; St Ms Webb). Joseph’s Hospital Regional Virology Laboratory, Hamil- Corresponding Author: Mark Loeb, MD, MSc, For editorial comment see p 1903. ton (Dr Mahony and Ms Chong); Departments of Pa- McMaster University, 1200 Main St W, Hamilton, ON thology and Microbiology and Immunology, University L8N 3Z5, Canada ( ©2009 American Medical Association. All rights reserved. (Reprinted) JAMA, November 4, 2009—Vol 302, No. 17 1865 Downloaded from at unknown institution on August 3, 2010
  3. 3. SURGICAL MASK VS N95 RESPIRATOR FOR PREVENTING INFLUENZA in nonexperimental settings is not well Nurses expected to work full-time able fit. The nurse was asked to wear understood.12 As a consequence, con- (defined as 37 hours per week) on the most comfortable mask for at least siderable uncertainty exists about the study units during the 2008-2009 in- 5 minutes to assess fit. Adequacy of the effectiveness of personal respiratory de- fluenza season were eligible. Nurses had respiratory fit was assessed using stan- vices against influenza for health care to provide current fit-test certifica- dard criteria, including chin place- workers. tion. Nurses who could not pass a fit ment, adequate strap tension, appro- During a pandemic, reducing trans- test were excluded from the study. The priate respirator size, fit across nose mission of influenza to health care research protocol was approved by the bridge, tendency of respirator to slip, workers may not only help support the McMaster University research ethics re- and position of mask on face and health care workforce, but may also pre- view board. All participants gave writ- cheeks. The nurse then conducted a vent influenza transmission to pa- ten informed consent. user seal check.17 Nurses had a quali- tients. Other personal protective strat- tative fit testing using the saccharin or egies, such as effective vaccines or Interventions Bitrex protocol.17 antiviral drugs, may be limited in avail- Randomization was performed cen- Nurses were asked to begin using the ability. Given the likelihood that N95 trally by an independent clinical trials surgical mask or N95 respirator when respirators will be in short supply dur- coordinating group such that investi- caring for patients with febrile respira- ing a pandemic and unavailable in many gators were blind to the randomiza- tory illness at the beginning of the in- countries, understanding the relative ef- tion procedure and group assignment fluenza season, which was defined as fectiveness of personal respiratory pro- and was stratified by center in per- 2 or more consecutive isolations of in- tective equipment is important. There muted blocks of 4 participants. It was fluenza per week in each study region. are few comparative studies of respira- not possible to conceal the identity of Nurses wore gloves and gowns when tory protective devices,13-15 and data the N95 respirator or the surgical mask entering the room of a patient with fe- comparing the surgical mask with the since manipulating these devices would brile respiratory illness, which was rou- N95 respirator among health care work- interfere with their function. Labora- tine practice. For aerosol-generating ers are sparse. tory personnel conducting hemagglu- procedures (such as intubation or bron- We conducted a randomized trial to tinin inhibition assays, polymerase choscopy), as long as tuberculosis was compare the surgical mask with the chain reaction (PCR), and viral cul- not suspected, nurses continued to use N95 respirator in health care workers. ture for influenza were blinded to al- the respiratory device they were as- We hypothesized that the surgical location. Nurses allocated to the sur- signed to. mask, which is less expensive and more gical mask group were required to wear We had planned to stop the study at widely available than the N95 respira- the brand of surgical mask already in the end of influenza season. However, tor, offers similar protection to the N95 use at their hospital. Following the se- because of the 2009 influenza A(H1N1) respirator among health care workers vere acute respiratory syndrome (SARS) pandemic, the study was stopped on at highest risk for exposure to influ- outbreak in Ontario, use of such a sur- April 23, 2009, when the Ontario Min- enza. gical mask was required by the Minis- istry of Health and Long-Term Care rec- try of Health and Long-Term Care when ommended N95 respirators for all METHODS providing care to or when within 1 m health care workers taking care of pa- Participants of a patient with febrile respiratory ill- tients with febrile respiratory illness. We enrolled nurses who worked in ness, defined as symptoms of a body emergency departments, medical units, temperature 38°C or greater and new Follow-up and pediatric units in 8 Ontario ter- or worsening cough or shortness of All participants were assessed for signs tiary care hospitals, of which 6 were breath.16 Nurses were instructed in and symptoms of influenza twice within the greater Toronto area. Six of proper placement of the surgical mask weekly using Web-based question- the 8 hospitals were university- according to the manufacturer’s naires. Response to the questionnaire affiliated teaching hospitals (range of recommendations. was monitored centrally and partici- bed size, 310-400) and 2 were commu- Since fit testing is mandatory for pants who failed to provide a response nity hospitals (bed sizes, 256 and 400). nurses in Ontario, the majority of were contacted and asked to complete Participants were enrolled from a total nurses in the study had been fit tested the questionnaire. If a new symptom of 22 units, which included 9 acute prior to enrollment; additional fit test- was reported, the study nurse was no- medical units, 7 emergency depart- ing was conducted for nurses who had tified and a flocked nasal specimen (Co- ments, and 6 pediatric units. There were not been fit tested in 2008. Using a stan- pan Italia, Brescia, Italy) was obtained an average of 34 beds (range, 14-60 dard protocol, a technician showed the by the participants. They were trained beds) on the medical units and an av- participant how to position the respi- to insert the swab into the left or right erage of 27 beds (range, 19-38) on the rator and fasten the strap and deter- nostril and rotate the swab at least 3 pediatric units. mine whether it provided an accept- times and to conduct self-swabbing if 1866 JAMA, November 4, 2009—Vol 302, No. 17 (Reprinted) ©2009 American Medical Association. All rights reserved. Downloaded from at unknown institution on August 3, 2010
  4. 4. SURGICAL MASK VS N95 RESPIRATOR FOR PREVENTING INFLUENZA any of 1 of the following symptoms or Secondary outcomes included detec- ference in the incidence of laboratory- signs were present: fever (tempera- tion of the following noninfluenza vi- confirmed influenza between the N95 ture 38°C), cough, nasal conges- ruses by PCR: parainfluenza virus types respirator group and surgical mask tion, sore throat, headache, sinus prob- 1, 2, 3, and 4; respiratory syncytial vi- group was estimated and the corre- lems, muscle aches, fatigue, earache, ear rus types A and B; adenovirus; meta- sponding 2-sided 95% confidence in- infection, or chills. We also provided pneumovirus; rhinovirus-enterovirus; terval (CI) was calculated. We used the participants with tympanic thermom- and coronaviruses OC43, 229E, SARS, Fisher exact test to assess statistical sig- eters. To assess household exposures NL63, and HKU1. Influenza-like ill- nificance in contingency tables hav- between study groups, we asked par- ness was defined as the presence of ing expected cell frequencies less than ticipants whether household mem- cough and fever (temperature 38°C).19 5. Noninferiority to the N95 respira- bers (spouses, roommates, or chil- Work-related absenteeism and physi- tor was achieved if the lower limit of dren) had experienced influenza-like cian visits for respiratory illness were also the 95% CI for the reduction in inci- illness over the study period. assessed. dence (N95 respirator minus surgical group) was greater than the prespeci- Outcomes Audits fied noninferiority limit of −9%. As- The primary outcome of this study was To assess compliance of participants suming an event rate of 20% in con- laboratory-confirmed influenza. This with the assigned mask or N95 respira- trols, this limit was selected on a clinical was defined by either the detection of tor, we conducted audits during what we basis considering that laboratory- viral RNA using reverse-transcriptase anticipated was peak influenza period, confirmed influenza would include (RT) PCR from nasopharyngeal and from March 11 to April 3, 2009. Medi- asymptomatic cases in addition to flocked nasal specimens or at least a cal and pediatric hospital study units at symptomatic cases of influenza. Infec- 4-fold rise in serum antibodies to cir- all centers with nurses participating in tion detected by serology can account culating influenza strain antigens. All the study were contacted by telephone for up to 75% of cases of laboratory- nasopharyngeal or nasal specimens daily by a research assistant to assess confirmed influenza where febrile ill- were tested for influenza and other res- whether there were patients admitted to ness is not present.21 piratory viruses with the xTAG Respi- the unit in droplet precautions for in- Since we did not anticipate severe ratory Virus Panel test (Luminex Mo- fluenza or febrile respiratory illness. If outcomes (eg, mortality) in the study lecular Diagnostics, Toronto, Ontario, there were such cases and if the pri- sample, we used a similar approach for Canada).18 This multiplex PCR assay mary nurse for the patient was en- influenza-like illness, work-related ab- detects influenza A virus subtypes H1 rolled in our study, a trained auditor was senteeism, and physician visits for res- (seasonal), H3, and H5 as well as the sent to the unit to observe for compli- piratory illness. All participants who majority of other viruses that cause res- ance. The auditor was instructed to stand had follow-up data collected (ie, had not piratory illness in humans. a short distance from the patient isola- withdrawn prior to any follow-up af- Blood specimens for serology were tion room to remain inconspicuous but ter they had been randomized) were in- obtained prior to enrollment and at the within distance to accurately record the cluded in the analysis. Since intention- end of the follow-up period. Serologi- audit. Auditors were asked to remain on to-treat analyses in noninferiority trials cal infection was defined by detection the unit until they recorded the type of may be biased toward finding no dif- of 4-fold or greater increase in influ- protective equipment worn by the par- ference, we also conducted an analy- enza-specific hemagglutinin inhibi- ticipant prior to the participant enter- sis of our primary outcome using only tion assay titer between baseline and ing the isolation room. data from participants with complete convalescent serum samples using To maintain patient confidentiality follow-up.22 guinea pig erythrocytes and the antigens and to remain anonymous to the study To avoid lack of independence as- circulating A/Brisbane/59/2007(H1N1)- participant, no audits were conducted sociated with counting multiple out- like virus; A/Brisbane/10/2007(H3N2)- within the patient’s room. Once an au- comes, each specific outcome in a par- like virus; B/Florida/4/2006-like vi- dit was conducted, the session was com- ticipant was only counted once. With rus; and A/TN/1560/09(H1N1), the pleted. Audits were conducted both on a power of 90% and a 2-sided type-I er- circulating pandemic influenza virus. weekdays and on weekends during day ror rate of 5%, the required sample For A/Brisbane/59/2007(H1N1)-like and evening shifts. Assessment of hand would be 191 participants in each group virus, A/Brisbane/10/2007(H3N2)- hygiene was not conducted. for a noninferiority test assuming an ab- like virus, and B/Florida/4/2006-like vi- solute risk reduction of 12% in the N95 rus, we restricted serological criteria of Statistical Analysis respirator group compared with the sur- infection to nurses who did not re- The effectiveness of the surgical mask gical mask. If the absolute reduction ceive the trivalent 2008-2009 influ- was assessed through a noninferiority was assumed to be 10%, a statistical enza vaccine to reduce misclassifica- analysis relative to the N95 respira- power of 80% would be maintained. tion due to vaccine response. tor.20 For the primary analysis, the dif- The absolute risk reductions selected ©2009 American Medical Association. All rights reserved. (Reprinted) JAMA, November 4, 2009—Vol 302, No. 17 1867 Downloaded from at unknown institution on August 3, 2010
  5. 5. SURGICAL MASK VS N95 RESPIRATOR FOR PREVENTING INFLUENZA were based on consensus by clinician RESULTS gical mask and 221 to the N95 respi- investigators. Assuming a 10% drop- Between September 23, 2008, and De- rator (F IGURE ). The mean age of out rate, we estimated that a total of 420 cember 8, 2008, 478 nurses were as- participants was 36.2 years, 94% of participants would be needed. SAS ver- sessed for eligibility and 446 partici- them were female, and study groups sion 9.1.3 (SAS Institute, Cary, North pants from 8 centers in Ontario were were well balanced in terms of demo- Carolina) was used to conduct the enrolled. They were then randomly as- graphics (TABLE 1). Vaccination sta- analyses. signed the intervention, 225 to the sur- tus was similar: 68 participants (30.2%) in the surgical mask group and 62 Figure. Flow Diagram for Trial of Surgical Mask vs N95 Respirator (28.1%) in the N95 respirator group had received 2008-2009 trivalent inac- 478 Nurses assessed for eligibility tivated influenza vaccine. Follow-up began January 12, 2009, 32 Excluded and ended April 23, 2009. Mean (SD) 4 Ineligible (part-time) 1 Away during study period duration of follow-up was similar be- 3 Did not want to use a particular mask 2 Did not want blood drawn tween groups: 97.9 (16.1) days in the 22 Had no interest surgical group and 97.2 (18.0) days in the N95 respirator group. There were 446 Randomized 24 participants who withdrew from the study with no follow-up—13 in the sur- 225 Randomized to receive surgical mask 221 Randomized to receive N95 respirator 212 Received surgical mask 210 Received N95 respirator gical mask group and 11 in the N95 res- as randomized as randomized pirator group—because of resignation 13 Did not receive intervention 11 Did not receive intervention (withdrew prior to follow-up) (withdrew prior to follow-up) or transfer (n = 5), working part-time 2 Transferred 1 Transferred 1 Switched to part-time 2 Resigned (n=1), no response (n=13), or illness 2 Had nonrespiratory illness 3 Had nonrespiratory illness (n=5) (Figure). None of the health care 8 Gave no reason 5 Gave no reason workers withdrew because of respira- 21 Lost to follow-up 19 Lost to follow-up tory illness. Of the resulting 422 (all of 3 Transferred 2 Transferred 2 Resigned 2 Resigned whom were in the analysis), fol- 4 Had nonrespiratory illness 4 Had nonrespiratory illness low-up was complete in 386 (91.4%), 11 Gave no reason 11 Gave no reason 1 Had no interest and 403 (95.5%) had acute and conva- lescent sera collected. There were 223 212 Included in analysis 210 Included in analysis nasal specimens obtained (115 in the 13 Excluded (withdrew prior to follow-up) 11 Excluded (withdrew prior to follow-up) surgical mask group and 108 in the N95 respirator group). Table 1. Characteristics of 446 Nurse Participants in the Surgical Mask and N95 Respirator Laboratory-confirmed influenza (by Groups RT-PCR or 4-fold rise in serum No. (%) titers) occurred in 50 nurses (23.6%) in the surgical mask group and in 48 Surgical Mask N95 Respirator Characteristic (n = 225) (n = 221) (22.9%) in the N95 respirator group Age, mean (SD) [range], y 36.5 (10.6) [21-62] 35.8 (10.6) [21-60] (absolute risk difference, −0.73%; Female sex 212 (94.2) 208 (94.1) 95% CI, −8.8% to 7.3%; P=.86), indi- Vaccinated against influenza 68 (30.2) 62 (28.1) cating noninferiority of the surgical 1 Coexisting conditions 22 (9.8) 26 (11.8) mask (T ABLE 2). The diagnosis of Asthma 10 (4.4) 12 (5.4) influenza was made by RT-PCR in 6 Diabetes 3 (1.3) 6 (2.7) nurses (2.8%) in the surgical mask Metabolic 2 (1.0) 4 (1.8) group (5 influenza A and 1 influenza Immunocompromised a 3 (1.3) 3 (1.3) B) and 4 (1.8%) in the N95 respirator Pregnancy 5 (2.2) 2 (0.9) group (1 influenza A and 3 influenza Other b 6 (2.7) 3 (1.3) B) (absolute risk difference, −0.93%; Distribution by hospital unit 95% CI, −3.82% to 1.97%; P = .75). Medical 55 (24.4) 52 (23.5) Four of the influenza A cases detected Pediatric 58 (26.2) 62 (28.1) by PCR were H1 (all in the surgical Emergency 112 (49.8) 107 (48.4) mask group). The serology results are a Immunosuppressive medications for transplantation (n=1), rheumatoid arthritis (n=3), uveitis (n=1), and Crohn dis- ease (n=1). summarized in Table 2. Notably, 8.0% b Includes chronic renal failure (n=1), coronary artery disease (n=1), liver disease (n=2), seizures/brain disorder (n=2), in the surgical mask group and 11.9% and connective tissue disease (n=4). in the N95 respirator group had a 1868 JAMA, November 4, 2009—Vol 302, No. 17 (Reprinted) ©2009 American Medical Association. All rights reserved. Downloaded from at unknown institution on August 3, 2010
  6. 6. SURGICAL MASK VS N95 RESPIRATOR FOR PREVENTING INFLUENZA 4-fold or greater rise in serum titers to 31 (70.5%) in the N95 respirator group two participants (19.8%) in the surgi- A/TN/1560/09(H1N1), the circulating had no symptoms. cal mask group reported an episode of pandemic swine influenza strain. There were 13 physician visits (6.1%) work-related absenteeism compared Noninferiority was demonstrated for respiratory illness among those in with 39 (18.6%) in the N95 respira- between the surgical mask group and the surgical mask group compared with tory group (absolute risk difference, the N95 respirator group for 2009 13 (6.2%) in the N95 respirator group −1.24%; 95% CI, −8.75% to 6.27%; influenza A(H1N1) (absolute risk dif- (absolute risk difference, −0.06%; 95% P =.75) (Table 4). There were no epi- ference, 3.89%; 95% CI, −1.82% to CI, −4.53% to 4.65%; P = .98). Forty- sodes of lower respiratory tract infec- 9.59%; P=.18). When the analysis was conducted Table 2. Comparison of Laboratory-Confirmed Influenza Between the Surgical Mask and using only the data from participants N95 Respirator Groups with complete follow-up visits, labo- No. (%) ratory-confirmed influenza (by RT- Absolute Risk PCR or 4-fold rise in serum titers) oc- Surgical Mask N95 Respirator Difference, % P (n = 212) (n = 210) (95% CI) Value curred in 66 nurses (33.9%) in the Laboratory-confirmed influenza a 50 (23.6) 48 (22.9) −0.73 (−8.8 to 7.3) .86 surgical mask group and in 72 (37.7%) RT-PCR influenza A 5 (2.4) 1 (0.5) −1.88 (−4.13 to 0.36) .22 in the N95 respirator group (absolute RT-PCR influenza B 1 (0.5) 3 (1.4) 0.96 (−0.89 to 2.81) .37 risk difference, 3.85%; 95% CI, −5.71% 4-Fold rise in serum titers 25 (11.8) 21 (10) −1.79 (−7.73 to 4.15) .55 to 13.41%; P=.43), indicating nonin- A/Brisbane/59/2007 (H1N1) b feriority. 4-Fold rise in serum titers 42 (19.8) 49 (23.3) 3.52 (−4.32 to 11.36) .38 No adenoviruses; no respiratory syn- A/Brisbane/10/2007 (H3N2) b 4-Fold rise in serum titers 15 (7.1) 19 (9.0) 2.0 (−3.0 to 7.17) .46 cytial virus type A; and no parainflu- B/Florida/4/2006 b enza 1, 2, and 4 viruses were detected 4-Fold rise in serum titers 17 (8.0) 25 (11.9) 3.89 (−1.82 to 9.59) .18 by PCR. There were no significant dif- A/TN/1560/09 (H1N1) b ferences between the surgical mask and Abbreviations: CI, confidence interval; RT-PCR, reverse-transcriptase polymerase chain reaction. a Influenza detected by 1 or more of the following: RT-PCR A, RT-PCR B, and 4-fold rise in serum titers to A/Brisbane/ N95 respirator groups in respiratory 59/2007(H1N1), A/Brisbane/10/2007(H3N2), and B/Florida/4/2006. Serology includes only nonvaccinated nurses. b Includes both vaccinated and nonvaccinated nurses. Two hundred ninety-four nurses were not vaccinated (147 in each syncytial virus type B, metapneumovi- group). rus, parainfluenza 3, rhinovirus- enterovirus, or coronoviruses. The lower CIs for the differences were Table 3. Comparison of RT-PCR Results for Other Respiratory Viruses Between the Surgical greater than −9%, meeting our criteria Mask and N95 Respirator Groups for noninferiority (TABLE 3). All 52 No. (%) (100%) of those having infection with Absolute Risk Surgical Mask N95 Respirator Difference, % P a respiratory virus other than influ- (n = 212) (n = 210) (95% CI) Value enza had 1 or more symptoms, but they Respiratory syncytial virus a 2 (0.9) 1 (0.5) −0.47 (−2.07 to 1.13) .99 did not meet the influenza-like illness Metapneumovirus 4 (1.9) 3 (1.4) −0.46 (−1.98 to 2.89) .99 definition. Parainfluenza virus b 1 (0.5) 2 (1.0) 0.48 (−1.12 to 2.09) .62 Nine nurses (4.2%) in the surgical Rhinovirus-enterovirus 8 (3.8) 10 (4.8) 0.99 (−2.87 to 4.85) .62 mask group and 2 nurses (1.0%) in the Coronavirus c 9 (4.3) 12 (5.7) 1.47 (−2.68 to 5.62) .49 N95 respirator group met our criteria Total d 20 (9.4) 22 (10.5) 1.04 (−4.67 to 6.76) .72 for influenza-like illness (absolute risk Abbreviations: CI, confidence interval; RT-PCR, reverse-transcriptase polymerase chain reaction. a Refers to respiratory syncytial virus type B only because no type A was detected. difference, −3.29%; 95% CI, −6.31% to b Refers to parainfluenza 3 only because no parainfluenza 1, 2, or 4 was detected. c Refers to coronaviruses OC43, 229E, NL63, and HKU1. 0.28%; P=.06) (TABLE 4). All 11 had d Totals are less than sums because more than 1 virus was detected in some participants. laboratory-confirmed influenza. A sig- nificantly greater number of nurses in the surgical mask group (12, or 5.66%) Table 4. Clinical Outcomes Between the Surgical Mask and N95 Respirator Groups reported fever compared with the N95 No. (%) respirator group (2, or 0.9%; P = .007). Absolute Risk Surgical Mask N95 Respirator Difference, % P There was no significant difference in (n = 212) (n = 210) (95% CI) Value nurses who reported cough, nasal con- Physician visits for respiratory 13 (6.1) 13 (6.2) −0.06 (−4.53 to 4.65) .98 gestion, headache, sore throat, myal- illness gia, fatigue, earache, or ear infection. Influenza-like illness a 9 (4.2) 2 (1.0) −3.29 (−6.31 to 0.28) .06 Of the 44 nurses in each group who had Work-related absenteeism 42 (19.8) 39 (18.6) −1.24 (−8.75 to 6.27) .75 influenza diagnosed by serology, 29 Abbreviation: CI, confidence interval. a Influenza-like illness was defined as the presence of both cough and temperature 38°C or greater. (65.9%) in the surgical mask group and ©2009 American Medical Association. All rights reserved. (Reprinted) JAMA, November 4, 2009—Vol 302, No. 17 1869 Downloaded from at unknown institution on August 3, 2010
  7. 7. SURGICAL MASK VS N95 RESPIRATOR FOR PREVENTING INFLUENZA tion among participants. There were no the N95 respirator.29 Based on the re- There are a number of limitations of adverse events reported by partici- sults of this trial, this concern does not this study. Compliance with the inter- pants. seem to be associated with an in- vention could not be assessed for all Fifty-five participants (25.9%) in the creased rate of infection of influenza or participants. Only 1 room entry was re- surgical mask group vs 47 (22.4%) in other respiratory viruses. corded per observation and the audi- the N95 respirator group reported a Influenza attack rates among health tor did not enter the isolation room to spouse or roommate with influenza- care workers in non-outbreak settings assess whether the participant re- like illness (P = .39). Forty-eight par- are sparse. Our data provide estimates moved the respirator protection. Au- ticipants (22.6%) in the surgical mask of an attack rate (23%) in a largely un- dits were only conducted on medical group vs 43 (20.5%) in the N95 respi- vaccinated cohort of nurses followed and pediatric units, not in the emer- rator group reported a child with in- closely during a period of relatively mild gency department. Had there been poor fluenza-like illness (P= .59). influenza-like illness and into the be- compliance with the N95 respirator, Over the 2-week audit period, ginning of what is now considered a this could have biased the study to- there were 18 episodes of patients pandemic period. Given that serology ward noninferiority. However, the re- admitted to units in droplet precau- captures exposure over the entire sea- sults from our audited sample suggest tions for influenza or febrile respira- son and that nurses have repeated ex- excellent adherence. This is in keep- tory illness where the nurse provid- posures, this rate of infection was not ing with the fact that all hospitals in the ing care for the patient had been unexpected. Our serological data in un- study were in Ontario, which was af- enrolled in our study. The results of vaccinated nurses were 20% for H3N2, fected by the SARS outbreak and where the audit demonstrated that all 11 10% for H1N1, and 8% for influenza B. use of personal protective equipment participants (100%) allocated to sur- In a community-based study, age- is mandated and audited by the On- gical masks and 6 of 7 participants specific rates of infection for those aged tario Ministry of Labour. (85.7%) allocated to N95 respirators 30 to 39 years by serology was 16% for We acknowledge that our protocol were wearing the device to which H3N2, approximately 5% for H1N1, did not account for the effect of indi- they had been assigned. and 5% for influenza B.21 It is for this rect contact because hand hygiene and reason that the number of partici- use of gloves and gowns were not moni- COMMENT pants with influenza-like illness, de- tored. An imbalance in hand hygiene Our data show that the incidence of fined by fever and cough alone,19 were between study groups, with worse ad- laboratory-confirmed influenza was relatively few compared with the num- herence in the N95 group, would have similar in nurses wearing the surgical ber with laboratory-confirmed influ- biased the study toward noninferior- mask and those wearing the N95 res- enza. Given that there was no differ- ity. However, individual-level random- pirator. Surgical masks had an esti- ence in laboratory-confirmed influenza ization and stratified randomization mated efficacy within 1% of N95 res- between study groups, the higher pro- within hospitals would help balance any pirators. Based on the prespecified portion of nurses in the surgical mask differences in adherence to hand hy- definition, the lower CI for the differ- group with influenza-like illness, al- giene between study groups. Because ence in effectiveness of the surgical though not statistically significant, was the use of gloves and gowns when en- mask and N95 mask was within −9% unexpected. tering the room of a patient with fe- and the statistical criterion of noninfe- The results of seroconversion to 2009 brile respiratory illness was standard riority was met. That is, surgical masks influenza A(H1N1) (10%) was unex- practice in our study hospitals, vari- appeared to be no worse, within a pre- pected given that the convalescent ability of use would likely have been specified margin, than N95 respira- specimens were obtained from April 23 minimal. tors in preventing influenza. to May 15, 2009. This attack rate may It is also impossible to determine Transmission by small droplet spread suggest that 2009 influenza A(H1N1) whether participants acquired influ- would be compatible with greater pro- was circulating in Ontario before April enza due to hospital or community ex- tection with the N95 mask compared 2009. An alternative explanation for this posure. However, our data on house- with the surgical mask where effi- high rate of seroconversion may be hold exposure suggest that such ciency estimates range from 2% to 92% cross-reaction due to exposure to sea- exposures were balanced between in- for particles smaller than 20 µm in di- sonal H1N1. tervention groups. We acknowledge ameter.23-28 The fact that attack rates Strengths of this study include indi- that not surveying participants’ cowork- were similar may suggest that small vidual-level randomization, compre- ers about influenza-like illness was a aerosols did not dominate transmis- hensive laboratory-confirmed out- limitation. Since we did not collect in- sion. come assessment with PCR and formation on droplet isolation precau- One frequently cited concern about serological evaluation, follow-up over tions, a greater exposure of N95 respi- the surgical mask is its inability to ob- an entire influenza season, and excel- rator nurses vs surgical mask nurses to tain an appropriate seal compared with lent participant follow-up. patients on droplet precautions would 1870 JAMA, November 4, 2009—Vol 302, No. 17 (Reprinted) ©2009 American Medical Association. All rights reserved. Downloaded from at unknown institution on August 3, 2010
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