title: Low attack rate of novel influenza A (H1N1) virus infection among healthcare workers: a prospective study in a setting with an elaborated containment plan.
abstract: OBJECTIVE
  This study aimed to determine incidence rates of novel influenza A (H1N1) infection among healthcare personnel with different exposure risks during the 2009 H1N1 pandemic.
  
  
  METHODS
  From August 2009 until April 2010, 66 healthcare workers from a 410 bed teaching hospital in Amsterdam were monitored. The following three different exposure groups were created: a high- (n = 26), intermediate- (n = 20), and low-risk group (n = 20). Throat swabs were collected each week and analyzed by real-time reverse transcriptase-polymerase chain reaction (RT-PCR) in order to detect the H1N1 virus. Blood was drawn at study enrollment and once monthly thereafter, and serum specimens were tested with an H1N1-specific hemagglutination-inhibition serologic assay. Influenza-like signs and symptoms were assessed weekly.
  
  
  RESULTS
  One of 26 high-risk group participants proved H1N1 positive once by RT-PCR. This corresponds to an incidence rate in the high-risk group of 5.7/1,000 person weeks (95% CI 0-17/1,000). None of the intermediate- and low-risk group participants proved H1N1 positive by RT-PCR. Significant antibody titer rises in convalescent sera were demonstrated in three participants: one was a confirmation of the case that had proved H1N1 positive by RT-PCR; the others occurred in two asymptomatic participants belonging to the low- and high-risk groups. An influenza-like illness was assumed in four participants from the high- (n = 1), intermediate- (n = 1) and low-risk (n = 2) groups; these findings were not confirmed by positive results from either diagnostic test.
  
  
  CONCLUSIONS
  This study demonstrates a low incidence rate of influenza A (H1N1) infection among healthcare workers during the 2009 H1N1 pandemic in a setting with high hygiene standards.
authors.affiliation: Department of Internal Medicine, Slotervaart Hospital, Louwesweg 6, 1066 EC, Amsterdam, The Netherlands. patrickmsmit@gmail.com
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Smit
authors.forename: Jan W
authors.initials: JW
authors.lastname: Mulder
authors.forename: Mohamed
authors.initials: M
authors.lastname: Ahdi
authors.forename: Ron
authors.initials: R
authors.lastname: Gerritsen
authors.forename: Stanley
authors.initials: S
authors.lastname: Darma
authors.forename: Paul H M
authors.initials: PH
authors.lastname: Smits
authors.forename: Chris
authors.initials: C
authors.lastname: Roggeveen
authors.forename: Eric C M
authors.initials: EC
authors.lastname: van Gorp
authors.forename: Guus F
authors.initials: GF
authors.lastname: Rimmelzwaan
authors.forename: Dees P M
authors.initials: DP
authors.lastname: Brandjes
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006784:Hospitals, Teaching; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control / Q000821:virology; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D016273:Occupational Exposure; D010564:Personnel, Hospital; D011159:Population Surveillance; D011446:Prospective Studies; D060888:Real-Time Polymerase Chain Reaction; D055815:Young Adult