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Volume 17, Number 8—August 2011

CME ACTIVITY

Risk Factors for Pandemic (H1N1) 2009 Seroconversion among Adults, Singapore, 2009

Wei-Yen LimComments to Author , Cynthia H.J. Chen, Yi Ma, Mark I.C. Chen, Vernon J.M. Lee, Alex R. Cook, Linda W.L. Tan, Norberto Flores Tabo, Ian G. Barr, Lin Cui, Raymond T.P. Lin, Yee Sin Leo, and Kee Seng Chia
Author affiliations: Author affiliations: National University of Singapore, Singapore (W.-Y. Lim, C.H.J. Chen, Y. Ma, M.I.C. Chen, V.J.M. Lee, L.W.L. Tan, N. Flores Tabo, Jr., K.S. Chia); Tan Tock Seng Hospital, Singapore (M.I.C. Chen, Y.S. Leo); Ministry of Defence, Singapore (V.J.M. Lee); National University of Singapore, Singapore (A.R. Cook); World Health Organization Collaborating Centre for Reference and Research on Influenza, Melbourne, Victoria, Australia (I. Barr); Ministry of Health, Singapore (L. Cui, R.T.P. Lin)

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Table A1

Bivariate and multivariate analyses of factors associated with seroconversion, Bivariate logistic regression of sociodemographic and individual variables, Multivariate logistic regression analysis of factors associated with seroconversion

Mean HR
(95% CI)† Mean
p value‡ Mean HR
(95% CI)† Mean
p value‡
Age, y
Mean 41.14 44.05 0.79 (0.65–0.95) 0.034
Median 43 45
Range 21–64 21–82
Age group, y
20–29 21 (16.9) 103 (83.1) 1.00 1.00
30–39 16 (14.2) 97 (85.8) 0.84 (0.42–1.67) 0.627 1.10 (0.52–2.36) 0.772
40–49 42 (16.2) 218 (83.8) 0.78 (0.44–1.39) 0.423 0.94 (0.46–1.94) 0.780
50–59 15 (9.7) 140 (90.3) 0.51 (0.25–1.03) 0.096 0.63 (0.29–1.34) 0.259
>60 4 (5.3) 71 (94.7) 0.25 (0.07–0.86) 0.054 0.31 (0.09–1.12) 0.105
Sex
F 52 (12.0) 380 (88.0) 1.00 1.00
M 46 (15.6) 249 (84.4) 1.48 (0.95–2.29) 0.128 2.23 (1.26–3.93) 0.024
Ethnicity
Chinese 6 (6.7) 84 (93.3) 1.00 1.00
Malay 56 (16.9) 275 (83.1) 2.76 (1.14–6.69) 0.054 2.67 (1.04–6.91) 0.075
Indian 34 (11.4) 265 (88.6) 1.55 (0.61–3.91) 0.390 1.94 (0.74–5.09) 0.218
Other 2 (28.6) 5 (71.4) 2.19 (0.26–18.54) 0.482 2.65 (0.30–23.52) 0.400
Dwelling type
≤3-room public housing 21 (11.9) 156 (88.1) 1.00 1.00
4-room public housing 51 (16.5) 259 (83.5) 1.58 (0.88–2.83) 0.173 1.39 (0.75–2.61) 0.348
5-room public housing or private
housing 26 (10.8) 214 (89.2) 1.08 (0.57–2.06) 0.763 1.01 (0.50–2.05) 0.800
Smoking
Current smoker 30 (20.1) 156 (79.1) 1.00 1.00
Nonsmoker/former smoker 68 (11.8) 156 (88.1) 0.52 (0.32–0.83) 0.027 0.64 (0.35–1.14) 0.171
Household members
1 63 (12.7) 433 (87.3) 1.00
2 33 (16.9) 162 (83.1) 1.34 (0.78–2.29) 0.371
3 2 (6.1) 31 (93.9) 0.89 (0.17–4.98) 0.666
4 0 3 (100.0) 0.400
Self-reported previous influenza vaccination
No 88 (13.3) 574 (86.7) 1.00 1.00
Yes 10 (15.4) 55 (84.6) 1.06 (0.51–2.22) 0.758 1.13 (0.51–2.48) 0.721
Employment outside the home
No 42 (15.2) 235 (84.8) 1.00 1.00
Yes, without anyone at work
having ARI symptoms during
study period 39 (11.2) 310 (88.8) 0.66 (0.41–1.08) 0.142 0.39 (0.21–0.70) 0.013
Yes, with anyone at work having
ARI symptoms during study period 17 (16.8) 84 (83.2) 1.18 (0.65–2.17) 0.605 0.89 (0.44–1.80) 0.715
Baseline antibody titer
Mean 0.082 0.272 0.54 (0.29–1.00) 0.086 0.50 (0.27–0.94) 0.059
Median 0 0
No. household members 0–4 y
Mean 0.204 0.291 0.79 (0.52–1.20) 0.287 0.71 (0.45–1.12) 0.166
Median 0 0
Range 0–3 0–3
No. household members 5–19 y
Mean 1.57 1.22 1.19 (1.02–1.40) 0.064 1.17 (0.95–1.43) 0.170
Median 1.0 1
Range 0–6 0–5
No. household members >19 y
Mean 3.33 3.10 1.14 (0.98–1.33) 0.131 1.13 (0.94–1.36) 0.216
Median 3 3
Range 1–8 1–9
Household contact with ARI symptoms during course of study
No 72 (14.4) 428 (85.6) 1.00 1.00
Yes 26 (11.5) 201 (88.5) 0.75 (0.46–1.22) 0.279 0.71 (0.41–1.21) 0.243
Travel out of Singapore during study period
No 50 (10.2) 438 (89.8) 1.00 1.00
Yes 48 (20.1) 191 (79.9) 2.10 (1.35–3.25) 0.012 1.76 (1.11–2.78) 0.044
Public transport
Seldom 26 (10.4) 223 (89.6) 1.00 1.00
Frequent 72 (15.1) 406 (84.9) 1.61 (0.96–2.70) 0.106 1.81 (1.05–3.09) 0.062

*Values are no. (%) except as indicated. Multivariate model included all variables listed; goodness-of-fit was 0.625. Boldface indicates significance. HR, hazard rate; CI, confidence interval; ARI, acute respiratory infection.
†Calculated as the mean HR of 1,000 separate analyses, where each analysis comprised 610 persons from different households; 1 person was randomly selected from households that had >1 member in the study. The means of the upper and lower bound of the 95% CIs were computed for each variable.
‡The mean of the p estimate from the 1,000 iterations was computed for each variable.

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