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Table 1 Cross-tabulations of seroconversion for influenza viruses circulating worldwide during the study period for n = 602 long-term Dutch travelers, 2009 to 2012

From: Influenza in long-term Dutch travelers in the tropics: symptoms and infections

Variables Total respondents N Seroconversion for any virusa A/California/007/09 H1N1pdm [H1pdm09] A/Brisbane/59/07 [H1N1] A/Brisbane/10/07 [H3N2] A/Perth/16/09 [H3N2] B/Florida/4/06 B/Brisbane/60/08
n n/N% p value n n/N% p value n n/N% p value n n/N% p value n n/N% p value n n/N% p value n n/N% p value
Total 602 90 15 N/A 43 7 N/A 16 3 N/A 26 4 N/A 34 6 N/A 12 2 N/A 11 2 N/A
Age-group                       
 <25 years of age 249 36 14   16 6   5 2   9 4   17 7   4 2   3 1  
 25–28 years 169 39 23   22 13   7 4   10 6   9 5   5 3   5 3  
 > = 29 years 184 15 8 <0.001* 5 3 0.001* 4 2 0.366 7 4 0.482 8 4 0.531 3 2 0.571 3 2 0.410
Gender                       
 Female 389 63 16   31 8   12 3   17 4   24 6   5 1   5 1  
 Male 213 27 13 0.247 12 6 0.287 4 2 0.379 9 4 0.933 10 5 0.454 7 3 0.093 6 3 0.180
Major travel flu zone                       
 Southeast Asia 252 39 15   16 6   3 1   11 4   17 7   5 2   5 2  
 Central & South America 222 36 16   20 9   10 5   9 4   10 5   5 2   5 2  
 Asia, other 21 2 10   1 5   0 0   0 0   0 0   1 5   0 0  
 Africa 107 13 12 0.687 6 6 0.580 3 3 0.132 6 6 0.702 7 7 0.469 1 1 0.679 1 1 0.771
  1. Age was summarized into tertiles: <25 years, 25–28 years and > =29 years. N/A Not Applicable
  2. aIn 10 individuals where the pre-travel titre was ≥40 there was evidence of re-infection (4 fold rise in antibody titre)
  3. P value throughout is Pearson’s chi-squared; Significance assigned (*) at p < 0.01