Infection in Health Personnel with High and Low Levels of Exposure in a Hospital Setting during the H1N1 2009 Influenza A Pandemic

Abstract

A novel H1N1 influenza A virus caused the first pandemic of the 21st century in 2009. Hospitals had an increased demand of health consultations, that made it difficult to estimate the incidence of infection in hospital personnel due to asymptomatic presentations and the under notification of cases. To estimate and compare the rate of exposure of high versus low risk health personnel to 2009 pandemic H1N1 (H1N1pdm2009) influenza A virus in a University Hospital in Chile, we performed a comparative and prospective study. Serum samples were obtained from 117 individuals that worked in the emergency room (ER) and the operating room (OR) during the peak of the pandemic. Antibody titers were determined by the hemagglutination inhibition (HI) assay. Of the samples analyzed, 65% were workers at the ER and 35% at the OR. Of the total number of the subjects tested, 29.1% were seropositive. One out of 3 (36.8%) workers at the ER had positive HI titers, meanwhile only 1 out of 7 (14.6%) workers from the OR was seropositive to the virus. The possibility of being infected in the ER as compared to the OR was 3.4 times greater (OR 3.4; CI 95%, 1.27-9.1), and the individuals of the ER had almost twice as much antibody titers against H1N1pdm2009 than the personnel in the OR, suggesting the potential of more than one exposure to the virus. Of the 34 seropositive subjects, 12 (35.3%) did not develop influenza like illness, including 2 non-clinical personnel involved in direct contact with patients at the ER. Considering the estimated population attack rate in Chile of 13%, both groups presented a higher exposure and seropositive rate than the general population, with ER personnel showing greater risk of infection and a significantly higher level of antibodies. This data provide a strong rationale to design improved control measures aimed at all the hospital personnel, including those coming into contact with the patients prior to triage, to prevent the propagation and transmission of respiratory viruses, particularly during a pandemic outbreak.

Fig 1. Seropositivity of health personnel to H1N1pdm2009 exposure during the pandemic outbreak in Chile.

Post pandemic antibody titer of high risk (ER) and low risk health personnel (OR) at the PUC Clinical Hospital in Santiago of Chile, against (A) A/California/07/2009 H1N1pdm, (B) A/Brisbane/10/2007 H3N2 strains and (C) A/Brisbane/59/2007 seasonal H1N1. Serum samples were obtained at least 3 weeks after the pandemic period in Chile (after epidemiological week 33) and before H1N1pdm2009 vaccination (November to March of 2010). Grey dots depict individual HI titer, and black lines represent the mean titer for each group. Discontinuos grey line, indicates the assay threshold of detection set to 10 HIU. Statistical significance was determined by an Unpaired t-test with Welch's correction (* p 0.0405).