Were health care workers with patient contact at greater risk of being infected with influenza in the 2009 pandemic?Archived

  Alagappan K, Silverman RA, Hancock K, Ward MF, Akerman M, Dawood FS, et al. Seropositivity for influenza A(H1N1)pdm09 virus among front line health care personnel. Emerg Infect Dis [Internet]. 2013 Jan [date cited]. http://dx.doi.org/10.3201/eid1901.111640

This small study performed at two tertiary care teaching hospitals in New York, compares and evaluates the risk of Influenza A (H1N1) pdm09 infection among front line health care professionals and non health care professionals in the 2009 pandemic. The possibility of carrying out this study occurred shortly following the appearance of H1N1 pdm09.  New York was chosen as the first highly populated area in the United States where an Influenza A (H1N1) pmd09 outbreak took place. 

Participants in this study were A(H1N1)pdm09 virus naive health care professionals (working front line, either at the emergency department or specially assigned influenza areas) as well as non health care personnel from the same community.  The study was undertaken in the  first wave of the pandemic  in the US between late April and early June 2009, well before any vaccine was available. The researchers found that out of the 193 health care professionals included in the study, 41 (21.2 %) subjects ended up having serological evidence of infection  (having  Influenza A (H1N1)pmd09 virus antibodies).  Of these  12 (29.3%) reported no influenza like symptoms. Among 147 non health care professionals, 24 (16.3% of) individuals were found to be seropositive.

Following multivariate analysis and observation of the following variables, age, sex, seasonal influenza vaccination and presence of children <18 years of age at work or residing in the same household, a possible confounding variable which the researchers recognised for both subject groups was contact with children. Although a result lacking statistical significance, it was reported that there was a higher  seropositivity among doctors caring for children  (30.8%) compared to those attending adults (8.7%). In terms of non health care professionals, the seropositivity for antibodies to Influenza A (H1N1) pdm09 of subjects living with children was higher (54.2%) than those not residing with children (43.2%).

Although the sample size was small and hence the power of the study limited (it only allowed for detection of a =15% of variation in seropositivity for Influenza A (H1N1) pmd09 virus between health care professionals and no health care professionals) the study findings illustrate no greater risk among  front line health care workers with patient contact, with the possible exception of paediatric care staff.

ECDC Comment (31 October 2012)

The emergence of a pandemic virus gives some unique research opportunities and this small study is an example. Normally interpreting the presence of antibodies to influenza (seropositivity) in individuals is difficult. Does it mean the person was infected or immunised. If infected was it recently  or some time in the past  But serology undertaken early in a pandemic after the first wave can only be due to recent infection allowing investigation of the risk factors.

This is a small study but its finding are consistent with other studies, mostly in the Far East.(1-3)  These indicate that health care workers are not especially at risk of infection from the pandemic influenza of 2009. Community exposure could be just as risky, though of course it would be hoped that health care workers would be taking precautions to protect themselves and that may have reduced seropositivity. The exception to this could be staff caring for children.  

It is important not to over interpret this study. All pandemics are unique to themselves and what is true for pandemic 2009 will almost certainly not entirely apply to other pandemics and certainly not to seasonal influenza. For example the 2009 pandemic was unusual in tits transmission being so focused in children. (4)  In preparing this comment ECDC staff had an examination of the literature and could not find any equivalent European studies. If any readers are aware of these or have other comments they should be sent to influenza@ecdc.europa.eu