Table 2.
Risk Factors for Laboratory-confirmed Influenza Illness Among Cohort Participants
| Characteristic | Incidence Rate per 1000 PY of Follow-up (95% CI) | Univariable Analysisa | Multivariable Analysisa,b | ||
|---|---|---|---|---|---|
| IRR (95% CI) | P Value | IRR (95% CI) | P Value | ||
| Sex | |||||
| Male | 31.4 (16.9–58.3) | 1 | … | 1 | … |
| Female | 34.6 (22.1–54.2) | 1.21 (0.52–2.84) | .66 | 0.88 (0.40–1.93) | .74 |
| Age group, y | |||||
| 18–29 | 20.9 (8.7–50.2) | 1 | … | 1 | … |
| 30–39 | 39.9 (23.2–68.7) | 1.73 (0.60–4.97) | … | 1.55 (0.54–4.43) | … |
| ≥40 | 36.3 (20.1–65.6) | 1.33 (0.43–4.05) | .30 | 1.42 (0.47–4.28) | .70 |
| HIV status | |||||
| Uninfected | 14.5 (6.0–34.7) | 1 | … | 1 | … |
| Infected | 46.0 (30.8–68.6) | 3.21 (1.22–8.41) | .02 | 2.75 (1.02–7.44) | .03 |
| Medical history | |||||
| Previous pulmonary tuberculosis | 28.2 (23.3–51.1) | 0.82 (0.28–2.43) | .87 | … | … |
| Pneumonia in past 5 y | 54.3 (24.4–120.9) | 1.86 (0.75–4.57) | .14 | … | … |
| Body mass index <18.5 kg/m2 | 40.3 (13.0–125.0) | 0.81 (0.25–2.68) | .73 | … | … |
| Housing characteristics | |||||
| No. of children aged <5 y in household | … | … | … | ||
| 0 | 36.2 (22.8–57.5) | 1 | … | … | |
| 1 | 27.8 (13.9–55.6) | 0.77 (0.33–1.77) | … | ||
| ≥2 | 37.3 (12.0–115.5) | 1.03 (0.30–3.50) | .80 | … | |
| No. of individuals aged ≥5 y in household | … | … | … | ||
| 0–2 | 25.5 (10.6–61.3) | 1 | … | … | |
| 3–4 | 28.1 (15.1–52.3) | 1.10 (0.38–3.22) | … | … | |
| ≥5 | 44.7 (26.5–75.4) | 1.76 (0.63–4.87) | .41 | … | |
| Crowding indexc | |||||
| <1.5 | 16.3 (6.12–43.5) | 1 | … | 1 | … |
| 1.5–2.4 | 47.1 (28.8–76.8) | 2.88 (0.96–8.62) | … | 3.41 (1.12–10.36) | … |
| ≥2.5 | 32.0 (16.6–61.5) | 1.95 (0.60–6.35) | .11 | 2.06 (0.62–6.83) | .06 |
| Socioeconomic characteristics | |||||
| Highest level of education | … | … | … | ||
| Never attended/primary | 47.6 (30.0–75.6) | 1 | … | … | |
| Secondary/tertiary | 22.5 (12.5–40.7) | 0.47 (0.22–1.00) | .05 | … | |
| Employment | … | … | … | ||
| No | 49.6 (28.8–85.4) | 1 | … | … | |
| Yes | 26.4 (16.2–43.1) | 0.53 (0.26–1.11) | .09 | … | |
| Food security: difficulty obtaining food | |||||
| Never | 25.9 (13.9–48.2) | 1 | … | 1 | … |
| 1–2 times/mo | 20.7 (9.9–43.5) | 0.80 (0.30–2.10) | … | 0.71 (0.27–1.88) | … |
| >2 times/mo | 87.2 (49.5–153.6) | 3.35 (1.45–7.76) | .005 | 3.09 (1.30–7.36) | .006 |
Abbreviations: CI, confidence interval; HIV, human immunodeficiency virus; IRR, incidence rate ratio; PY, person-years.
aIRRs estimated for the incidence of laboratory-confirmed influenza, using Poisson regression.
bAdjusted for sex, age group, HIV status, crowding index, and food security.
cThe crowding index was calculated as the number of persons in the household divided by the number of sleeping rooms.