Do Frontline Healthcare Workers Have Increased Risk of Contracting Pandemic H1N1 2009 Influenza?

Background: Exposure of HCWs to patients with Pandemic H1N1 2009 influenza virus (H1N1pdm) is becoming more common as the pandemic progresses. Initially in the pandemic in Victoria, Australia, many patients with suspected H1N1pdm influenza were cared for in negative pressure airborne isolation with contact and droplet precautions. As cases increased, however, airborne isolation was no longer used, but contact and droplet precautions were continued.

Objective: To determine whether frontline healthcare workers (HCWs) are at greater risk of contracting H1N1pdm compared with a control group.

Methods: This was a prospective study at four large Melbourne public acute care hospitals comparing frontline HCWs with exposure to patients with H1N1pdm or influenza like illness (ILI) (emergency, infectious diseases, intensive care unit) (Clinical) with other hospital staff without patient contact, as a proxy for a community control group (Non-Clinical).

Blood samples were taken on all participants at study entry and at study exit only on participants that reported respiratory symptoms during the study period. Participants filled out a symptom and exposure questionnaire at study entry. If participants developed a respiratory illness, a nasal swab was taken.

Serum was tested for antibodies to H1N1pdm influenza virus using the haemagglutination inhibition assay with A/California/7/2009 virus and turkey red blood cells.  A titre of ≥1:40 was chosen as the cut off for likely H1N1pdm infection.  Real time PCR for influenza was performed on swabs taken from subjects with ILI using the CDC kits for the detection of seasonal and H1N1pdm influenza viruses.

Results: There were 446 participants in the study, 231 in the clinical and 215 in the non-clinical group. 32% of clinical participants were doctors, 58% nurses, 5% physiotherapists and 5% other, of whom 90% reported having contact with a patient with proven or suspected H1N1pdm influenza. Approximately 70% reported always using masks, gowns and gloves when caring for patients in droplet precautions, with only 30% always using face protection. Only one participant reported having infection with laboratory proven H1N1pdm influenza. 8% of clinical participants reported taking oseltamivir. 79/446 (18%) participants had an antibody titre of ≥1:40, 46/231 (20%) in the clinical and 33/215 (15%) in the non-clinical group (P=0.21). 56/446 (11%) participants had second bleed serology taken, with no new seroconversions. Twenty participants took 23 nasal swabs for respiratory symptoms, six of which were PCR positive for H1N1pdm influenza.

Conclusions: This highly exposed group of frontline healthcare workers caring for patients with suspected or proven H1N1pdm influenza were no more likely to have had H1N1pdm influenza infection than participants with no patient exposure. This suggests that personal protective measures were adequate in preventing transmission from patient to HCW.