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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. ChenComments to Author , Vernon J.M. Lee, Ian G. 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: 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); DSO National Laboratories, Singapore (B.H. Tan, J. Loh)

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Table 1

Selected characteristics of healthcare workers by seroconversion status for pandemic (H1N1) 2009, Singapore, 2009*

Characteristic
No. (%) seroconverters, n = 35
No. (%) nonseroconverters, n = 496
p value
Baseline sample timing 0.20†
Jun 22–26 17 (49) 187 (38)
Jun 28–Jul 7
18 (51)
309 (62)

Follow-up samples taken 0.73†
Intraepidemic only 3 (9) 65 (13)
Postepidemic only 2 (6) 31 (6)
Intraepidemic and postepidemic
30 (86)
400 (81)

Female
30 (86)
411 (83)
0.66†
Seasonal influenza vaccination 34 (97) 449 (91) 0.19†
ARI episode‡ 22 (63) 75 (15) <0.01†
FRI episode‡
18 (51)
41 (8)
<0.01†
Age, y, mean (95% CI) 35 (31–39) 34 (33–35) 0.76§
GMT for baseline sample (95% CI) 5.9 (5.3–6.5) 7.8 (7.3–8.3) 0.02§

*ARI, acute respiratory illness; FRI, febrile respiratory illness; CI, confidence interval; GMT, geometric mean titer.
†χ2 test comparing seroconverters and nonseroconverters.
‡Healthcare workers who seroconverted are considered to have had an ARI or FRI episode if the date of onset preseded the date when seroconversion was detected.
§Student t test comparing seroconverters and nonseroconverters.

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