Table 3 Risk of H7N9 and H5N1 virus infections in the 2013–2014 and 2014–2015 cohorts.

From: Avian influenza A(H7N9) and (H5N1) infections among poultry and swine workers and the general population in Beijing, China, 2013–2015

Virus type

Participant category

Number of infections†/person-months (‰)

Unadjusted IRR (95% CI), p value*

Adjusted IRR (95% CI), p value#

H7N9

Poultry workers

16/10099 (1.6)

35.13 (7.55–∞)‡ <0.001

34.90 (7.47–∞)‡ <0.001

Swine workers

0/11126 (0)

NA

NA

General population

0/15734 (0)

Reference

Reference

Overall

16/36959 (0.4)

  

H5N1 clade 2.3.4

Poultry workers

38/10099 (3.8)

9.85 (4.17–23.31) <0.001

10.58 (4.43–25.30) <0.001

Swine workers

4/11126 (0.4)

0.94 (0.27–3.34) 0.926

1.15 (0.32–4.11) 0.833

General population

6/15734 (0.4)

Reference

Reference

Overall

48/36959 (1.3)

  

H5N1 clade 2.3.2.1

Poultry workers

3/10099 (0.3)

2.33 (0.39–13.96) 0.353

2.06 (0.34–12.43) 0.432

Swine workers

2/11126 (0.2)

1.41 (0.20–10.03) 0.730

1.34 (0.19–9.55) 0.769

General population

2/15734 (0.1)

Reference

Reference

Overall

7/36959 (0.2)

  
  1. Note. IRR: incidence rate ratio; CI: confidence interval; NA: not available.
  2. †Seroconversion of antibody against H7N9 or H5N1 virus was considered as infection, and defined as a 4-fold or greater increase in antibody titer by hemagglutination-inhibition assay between paired serum specimens with a titer ≥1:40 for the second specimen.
  3. *Univariate Poisson regression model was used to compare person-month incidence rates of H7N9 or H5N1 virus infections between participant categories.
  4. #Multivariate Poisson regression model was used to compare person-month incidence rates of H7N9 or H5N1 virus infections between participant categories after adjusting for sex, age group and underlying disease status.
  5. ‡Exact conditional analysis was used to estimate the IRRs and 95% CIs.
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