Table 1. Demographic and exposure characteristics of study participants.

Characteristic	n (%)*
Age group (y)
<30	20 (24.1)
30–39	26 (31.3)
40–49	26 (31.3)
>49	11 (13.3)
Male sex	30 (36.1)
Residence in Hanoi City	81 (97.6)
Department
ICU†	37 (45.1)
Infectious diseases	30 (36.6)
Laboratory	8 (9.8)
Radiology	6 (7.3)
Hematology	1 (1.2)
Years smoked
None	64 (78.1)
<10	6 (7.3)
10–30	12 (14.6)
Chronic medical condition	22 (26.5)
Influenza vaccination in 2004	56 (68.3)
Oseltamivir since Dec 27, 2003	1 (1.2)
No. of H5N1 patients visited
0 (none)	4 (4.9)
1	3 (3.7)
2	31 (37.8)
3	32 (39.0)
4	4 (4.9)
5 (all)	8 (9.8)
Changed bedding
Yes	46 (59.0)
No	32 (41.0)
Touched patients
Yes	75 (96.2)
No	3 (3.9)
Exposure to H5N1 patient(s) who did not wear masks	57 (73.1)

*The no. of study participants (n) for each characteristic ranged from 78 to 83; percentage provided is based on the actual number of participants.
†ICU, intensive care unit.