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Volume 19, Number 6—June 2013

Research

Effect of Travel on Influenza Epidemiology

Sanne-Meike BelderokComments to Author , Guus F. Rimmelzwaan, Anneke van den Hoek, and Gerard J.B. Sonder
Author affiliations: Public Health Service, Amsterdam, the Netherlands (S.-M. Belderok, A. van den Hoek, G.J.B. Sonder); Academic Medical Centre, Amsterdam (S.-M. Belderok, A. van den Hoek, G.J.B. Sonder); Erasmus Medical Center, Rotterdam, the Netherlands (G.F. Rimmelzwaan); National Coordination Centre for Traveler’s Health Advice, Amsterdam (G.J.B. Sonder)

Main Article

Table 1

Infection with >1 influenza type in 1,190 travelers from the Netherlands to (sub)tropical countries, October 2006–October 2007*

Characteristic Travelers at risk, no. (%) Travelers with infection†
Person-months of travel IR, %‡ (95% CI) Univariable analysis
Multivariable analysis
No. AR, % (95% CI) IRR (95% CI) p value IRR (95% CI) p value
All 1,190 (100) 86 7.2 (5.9–8.8) 969 8.9 (7.1–10.9)
Sex
M 510 (43) 31 6.1 (4.2–8.4) 404 7.7 (5.3–10.8) 1.0 0.286
F 680 (57) 55 8.1 (6.2–10.4) 565 9.7 (7.4–12.6) 1.3 (0.8–2.0)
Age group, y
<25 140 (12) 8 5.7 (2.7–10.6) 151 5.3 (2.5–10.1) 1.00 0.098 1.0
25–34 381 (32) 22 5.8 (3.8–8.5) 315 7.0 (4.5–10.4) 1.3 (0.6–3.0) 1.3 (0.6–2.9) 0.558
35–44 223 (19) 21 9.4 (6.1–13.8) 168 12.5 (7.9–18.8) 2.4 (1.0–5.3) 2.2 (1.0–4.9) 0.063
45–54 226 (19) 13 5.8 (3.2–9.4) 165 7.9 (4.4–13.1) 1.5 (0.6–3.6) 1.3 (0.5–3.2) 0.538
55–64 165 (14) 17 10.3 (6.3–15.7) 124 13.7 (8.3–21.5) 2.6 (1.1–6.0) 2.6 (1.1–6.1) 0.025
>65 55 (5) 5 9.1 (3.4–19.0) 46 10.9 (4.0–24.1) 2.1 (0.7–6.3) 1.9 (0.6–5.8) 0.259
Region of birth
Western 1,103 (93) 72 6.5 (5.2–8.1) 905 8.0 (6.3–10.0) 1.0 0.006 1.0
Nonwestern
Africa 12 (1) 3 25.0 (6.8–54.1) 11 27.3 (6.9–74.2) 3.4 (1.1–10.8) 3.7 (1.2–11.9) 0.029
Latin America 47 (4) 9 19.1 (9.8–32.2) 31 29.0 (14.2–53.3) 3.7 (1.8–7.4) 3.8 (1.9–7.8) <0.001
Asia 28 (2) 2 7.1 (1.2–21.7) 22 9.1 (1.5–30.0) 1.1 (0.3–4.6) 1.1 (0.3–4.4) 0.926
Previous travel to(sub)tropical country
Never 224 (19) 11 4.9 (2.6–8.4) 180 6.1 (3.2–10.6) 1.0 0.140
1–5 times 687 (58) 49 7.1 (5.4–9.2) 573 8.6 (6.4–11.2) 1.4 (0.7–2.7)
>6 times 279 (23) 26 9.3 (6.3–13.2) 217 12.0 (8.0–17.3) 2.0 (1.0–4.0)
Primary purpose of travel
Tourism 1,017 (85) 73 7.2 (5.7–8.9) 826 8.8 (7.0–11.1) 1.0 1.000
Work or education 100 (8) 8 8 (3.8–14.6) 86 9.3 (4.3–17.7) 1.1 (0.5–2.2)
Visiting friends and/or relatives 73 (6) 5 6.9 (2.6–14.5) 57 8.8 (3.2–19.4) 1.0 (0.4–2.4)
Travel destination
Latin America
South America 202 (17) 13 6.4 (3.6–10.5) 167 7.8 (4.3–13.0) 1.0 0.373
Central America and Caribbean 120 (10) 9 7.5 (3.7–13.3) 78 11.5 (5.6–21.2) 1.5 (0.7–3.5)
Africa
Southern and Eastern Africa 181 (15) 12 6.6 (3.6–11) 147 8.2 (4.4–13.9) 1.1 (0.5–2.3)
Middle, Western, Northern Africa 110 (9) 10 9.1 (4.7–15.6) 75 13.3 (6.8–23.8) 1.7 (0.8–3.9)
Asia
Southeastern and Eastern Asia 416 (35) 25 6.0 (4.0–8.6) 365 6.9 (4.5–10.0) 0.9 (0.5–1.7)
South-central and Western Asia 125 (11) 14 11.2 (6.5–17.7) 97 14.4 (8.2–23.6) 1.9 (0.9–4.0)
More regions 33 (3) 3 9.1 (2.4–22.8) 37 8.1 (2.1–22.1) 1.1 (0.3–3.7)
More continents 3 (<1) 0 0
Symptoms
Fever
No 1,073 (90) 71 6.6 (5.2–8.2) 854 8.3 (6.5–10.4) 1.0 0.131
Yes 117 (10) 15 12.8 (7.6–19.8) 115 13.0 (7.6–21.0) 1.6 (0.9–2.7)
ILI§
No 1,150 (97) 77 6.7 (5.4–8.3) 930 8.3 (6.6–10.3) 1.0 0.010 1.0 0.004
Yes 40 (3) 9 22.5 (11.6–37.3) 38 23.7 (11.6–43.5) 2.8 (1.4–5.7) 2.8 (1.4–5.5)

*AR, attack rate; IR, incidence rate; IRR, incidence rate ratio; ILI, influenza-like illness. Boldface indicates significance (p<0.05).
†Travelers with confirmed influenza infection for >1 influenza virus.
‡Per 100 person-months.
§Travelers with ILI are a subgroup of travelers with fever.

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