Pandemic (H1N1) 2009 Seroconversion, Singapore | CDC EID

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Volume 16, Number 10–October 2010
Research
Risk Factors for Pandemic (H1N1) 2009 Virus Seroconversion among Hospital Staff, Singapore
Mark I.C. Chen , Vernon J.M. Lee, Ian Barr, Cui Lin, Rachelle Goh, Caroline Lee, Baldev Singh, Jessie Tan, Wei-Yen Lim, Alex R. Cook, Brenda Ang, Angela Chow, Boon Huan Tan, Jimmy Loh, Robert Shaw, Kee Seng Chia, Raymond T.P. Lin, and Yee Sin Leo
Author affiliations: Tan Tock Seng Hospital, Singapore (M.I.C. Chen, R. Goh, C. Lee, B. Singh, J. Tan, B. Ang, A. Chow, Y.S. Leo); Duke-National University of Singapore Graduate Medical School, Singapore (M.I.C. Chen); Ministry of Defence, Singapore (V.J.M. Lee); World Health Organization Collaborating Centre for Reference and Research on Influenza, Melbourne, Victoria, Australia (I. Barr, R. Shaw); National Public Health Laboratory, Singapore (C. Lin, R.T.P. Lin); National University of Singapore, Singapore (W.-Y. Lim, A.R. Cook, K.S. Chia); and DSO National Laboratories, Singapore (B.H. Tan, J. Loh)

Suggested citation for this article

Abstract
We describe incidence and risk factors for pandemic (H1N1) 2009 virus infection in healthcare personnel during the June–September 2009 epidemic in Singapore. Personnel contributed 3 serologic samples during June–October 2009, with seroconversion defined as a >4-fold increase in hemagglutination inhibition titers to pandemic (H1N1) 2009. Of 531 participants, 35 showed evidence of seroconversion. Seroconversion rates were highest in nurses (28/290) and lowest in allied health staff (2/116). Significant risk factors on multivariate analysis were being a nurse (adjusted odds ratio [aOR] 4.5, 95% confidence interval [CI] 1.0–19.6) and working in pandemic (H1N1) 2009 isolation wards (aOR 4.5, 95% CI 1.3–15.6). Contact with pandemic (H1N1) 2009–infected colleagues (aOR 2.5, 95% CI 0.9–6.6) and larger household size (aOR 1.2, 95% CI 1.0–1.4) were of borderline significance. Our study suggests that seroconversion was associated with occupational and nonoccupational risk factors.
During the 2003 epidemic of severe acute respiratory syndrome (SARS), large nosocomial outbreaks of SARS occurred in several hospitals in Singapore (1,2). Since then, concerns have been raised about how emerging infections, in particular respiratory infections, could result in transmission from patients to healthcare workers and vice versa, given the high frequency and intensity of healthcare worker contacts in the hospital environment (3). For pandemic influenza, additional concerns exist that even mild disease might result in staff absenteeism and, subsequently, would reduce staff strength at a time of increased demand for health services (4).

In April 2009, a novel influenza A virus, now referred to as pandemic (H1N1) 2009 virus, emerged in the United States and Mexico and rapidly spread worldwide (5–7). Published reports on pandemic (H1N1) 2009 in healthcare workers have attributed transmission to a mixture of healthcare and nonhealthcare exposures (8–10), with varying compliance to infection control measures implicated in some transmission events (9,11). Early data from the United States suggest that healthcare workers were not overrepresented among case reports of pandemic (H1N1) 2009 compared with cases in the general population (9), but the risk for infection for healthcare workers, and between different subgroups of healthcare workers, remains unclear (9).

During the initial epidemic wave of pandemic (H1N1) 2009 in Singapore, June–September 2009, we conducted a prospective seroepidemiologic cohort study among healthcare workers in Tan Tock Seng Hospital (TTSH), Singapore, by using serial blood specimens to determine antibody levels against pandemic (H1N1) 2009 as a marker of serologic infection. We describe the incidence of serologic evidence of infection and associated occupational and nonoccupational risk factors for infection in this cohort of healthcare workers.

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Pandemic (H1N1) 2009 Seroconversion, Singapore | CDC EID

Suggested Citation for this Article
Chen MIC, Lee VJM, Barr I, Lin C, Goh R, Lee C, et al. Risk factors for pandemic (H1N1) 2009 virus seroconversion among hospital staff, Singapore. Emerg Infect Dis [serial on the Internet]. 2010 Oct [date cited]. http://www.cdc.gov/EID/content/16/10/1554.htm

DOI: 10.3201/eid1610.100516


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Address for correspondence: Mark I.C. Chen, Department of Clinical Epidemiology, 11 Jalan, Tan Tock Seng Hospital, Singapore 308433; email: mark_ic_chen@ttsh.com.sg