Date: 04 Jun 2011

Low attack rate of novel influenza A (H1N1) virus infection among healthcare workers: a prospective study in a setting with an elaborated containment plan

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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.


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.


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.


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.