Results
A total of 239 cases with confirmed influenza AH1N1pmd09 virus infection and 239 matched controls were included. Cases had a mean age of 5.4 years (SD = ±4.5), 42.3 % were females, 88.9 % were Caucasian, 74.3 % had secondary or higher education, 36.6 % had parents smokers and only 0.9 % had received any influenza vaccine while 35.9 % had received at least one dose of pneumococcal vaccine and 32.7 % were fully vaccinated according to their age. Controls had similar characteristics with no significant differences (Table 1).
Cases presented a higher prevalence of underlying conditions such as pneumonia in the previous two years [OR = 3.23; 95 % CI: 1.38 – 7.58 p = 0.007], asthma [OR = 2.45; 95 % CI: 1.17 – 5.14 p = 0.02] and presenting more than 1 co morbidity [OR = 1.67; 95 % CI: 0.99 – 2.82 p = 0.05] (Table 1). The frequency of hand washing > 5 times [aOR = 0.62; 95 % CI: 0.39 – 0.99 p = 0.04] was the only statistically significant protective factor (Table 2).
Statifying the sample into two age groups (0–4 years and 5 to 17 years) the only statistically significant risk factor was having had pneumonia in the previous two years [OR = 6.00; 95 % CI: 1.34 – 26.81 p = 0.02], was (Table 3).
The school age group (5–17 years) showed a negative association for influenza infection for both washing more than 5 times per day [aOR = 0.47; 95 % CI: 0.22 – 0.99 p = 0.04] where in the 0–4 years group there was no significant association observed [aOR = 0.91; 95 % CI: 0.46 – 1.78 p = 0.77] and hand washing after touching contaminated surfaces [aOR = 0.19; 95 % CI: 0.04 – 0.86 p = 0.03] versus [aOR = 1.06; 95 % CI: 0.44 – 2.56 p = 0.77] in the 0–4 years group (Table 4)].
Stratifying the 0–4 age group into 0–2 years and 3–4 years, no significant differences were observed in cases and controls with respect to the questions referring to having received information regarding influenza prevention, frequency of daily hand washing or use of alcohol-based hand sanitizers or hand washing after touching potentially contaminated surfaces.