Table 4. Factors significantly associated with infection of pandemic (H1N1) 2009 virus in close contacts in multivariate analysis*.
| Factor | All close contacts† |
Flight passenger contacts‡ |
Nonflight passenger contacts§ |
|||||
|---|---|---|---|---|---|---|---|---|
| OR (95% CI) | p value | OR (95% CI) | p value | OR (95% CI) | p value | |||
| Age of close contacts, y | ||||||||
| >50 | Reference | Reference | Reference | |||||
| 20–50 | 3.42 (1.56–7.48) | 0.002 | 3.13 (0.40–24.76) | 0.280 | 2.89 (1.23–6.80) | 0.015 | ||
| 0–19 |
7.76 (3.52–17.09) |
<0.001 |
|
13.33 (1.77–100.22) |
0.012 |
|
4.97 (2.06–12.00) |
<0.001 |
| Relationship to index case-patient | ||||||||
| Nonhousehold member | Reference | NA | Reference | |||||
| Household member |
3.83 (2.65–5.53) |
<0.001 |
|
NA |
NA |
|
2.37 (1.58–3.55) |
<0.001 |
| Type of exposure to index case-patient | ||||||||
| During asymptomatic phase¶ | Reference | Reference | Reference | |||||
| During symptomatic phase |
1.86 (1.23–2.80) |
0.003 |
|
NA |
NA |
|
1.79 (1.09–2.93) |
0.021 |
| Exposure duration of close contacts, h | ||||||||
| <12 | Reference | Reference | Reference | |||||
| >12 | 1.83 (1.25–2.67) | 0.002 | 3.41 (1.49–7.78) | 0.004 | NA | NA | ||
*Variables with p<0.1 in Table 2 were included in multivariate unconditional logistic regression analysis. Hosmer-Lemeshow goodness-of-fit test was used to assess the model fit for logistic regression. OR, odd ratio; CI, confidence interval; NA, not available, indicating not included in the final model. †One dependent variable (infection with pandemic [H1N1] 2009 virus) and 5 independent variables (age of index case-patient, type of exposure to index case-patients, age of close contacts, relationships to index case-patients, and exposure duration of close contacts) were included in multivariate analysis. One independent variable (age of index case-patient) was removed in the stepwise regression equation. The goodness-of-fit test suggested that the logistic regression model fitted well (p = 0.631). ‡One dependent variable (infection with pandemic [H1N1] 2009 virus) and 4 independent variables (age of index case-patient, type of exposure to index case-patient, age of close contacts, and exposure duration of close contacts) were included in multivariate analysis. Two independent variables (age of index case-patient and type of exposure to index case-patient) were removed in the stepwise regression equation. The goodness-of-fit test suggested that the logistic regression model fitted well (p = 0.982). §One dependent variable (infection with pandemic [H1N1] 2009 virus) and 5 independent variables (age of index case-patient, type of exposure to index case-patient, age of close contacts, relationships to index case-patient, and exposure duration of close contacts) were included in multivariate analysis. Two independent variables (age of index case-patient and exposure duration of close contacts) were removed in the stepwise regression equation. The goodness-of-fit test suggested the logistic regression model fitted well (p = 0.751). ¶Exposed to symptomatic index case-patients before their illness onset or exposed to index case-patients who had subclinical infections.