Table 1.

Seroprevalence to influenza A/H1N1/2009 virus by potential risk group of transmission

Potential risk group of transmission	Sample proportion, n (%)	Age, mean ± SD	Seropositive subjects	Seropositivity prevalence, % (95% CI)a
Total sample	2222 (100%)	32.6 (21.4)	859	38.7% (36.7–40.7)
Risk groupb
Studentc	994 (45%)	14.9 (5.1)	470	47.3% (44.2–50.4)
Teacherd	360 (16%)	42.0 (10.3)	122	33.9% (29.2–38.9)
Healthcare workere	309 (14%)	38.1 (10.0)	76	24.6% (20.1–29.7)
Adult >60 yearsf	189 (9%)	82.3 (9.1)	69	36.5% (30.0–43.6)
General populationg	370 (17%)	40.6 (11.9)	122	33.0% (28.4–37.9)

SD, standard deviation; CI, confidence interval.

^aSeropositivity prevalence data represent percentage and 95% CI of individuals with positive antibodies in that group.

^bRisk group: groups according to potential risk of transmission of influenza A/H1N1/2009 virus; p-value = 0.011 obtained from a logistic regression model (backward, stepwise) adjusting for gender, age, and group.

^cStudent: from elementary school to college students.

^dTeacher: from elementary school to college teachers in contact with students for at least 6 h/day.

^eHealthcare worker: Doctors, nurses, lab personnel, and technicians in contact with patients for more than 8 h/day.

^fAdults >60 years: institutional home residents.

^gGeneral population: adults aged 20–60 years not included in the other groups and not pregnant.