Table 2. Results of influenza virus testing of nasal swab specimens from 732 study participants in the Influenza Cohort Study performed during 2009 pandemic, Toronto, Ontario, Canada*.
| Characteristic | Influenza test status |
||
|---|---|---|---|
| No. negative or not ill, n = 712† | No. positive, n = 20‡ | p value | |
| Mean age, y (± SD) | 42.9 (11.3) | 43.9 (9.3) | 0.69 |
| Female sex | 595/712 (83.6) | 16/20 (80.0) | 0.76 |
| Worker in acute care hospital |
550/712 (77.3) |
13/20 (65.0) |
0.28 |
| Recipient of vaccine | |||
| A(H1N1)pdm09 vaccine§ | 533/699 (76.3) | 2/20 (10.0) | <0.001 |
| Seasonal influenza vaccine 2009–10 | 258/712 (36.2) | 9/20 (45.0) | 0.42 |
| Seasonal influenza vaccine 2008–09 |
470/696 (67.5) |
13/20 (65.0) |
0.81 |
| Underlying health conditions | |||
| Asthma | 67/702 (9.5) | 2/20 (10.0) | 1.00 |
| Diabetes mellitus | 26/700 (3.7) | 1/20 (5.0) | 0.54 |
| Allergy to airborne irritants | 284/646 (44.0) | 11/18 (61.1) | 0.15 |
| Current smoker |
63/704 (9.0) |
3/20 (15.0) |
0.42 |
| Potential exposure conditions | |||
| Hand-to-face habits¶ | 337/705 (47.8) | 14/20 (70.0) | 0.05 |
| Wearing of prescription eyeglasses | 493/709 (69.5) | 12/20 (60.0) | 0.36 |
| Reusable water bottle use >1×/ wk | 307/705 (43.6) | 6/20 (30.0) | 0.23 |
| Public transit >8 trips per week | 236/706 (33.4) | 5/20 (25.0) | 0.43 |
| Group gathering attendance >1× | 655/710 (92.3) | 19/20 (95.0) | 1.00 |
| Face-to-face contacts/d, median (IQR) | 10 (5, 20) | 15 (8, 20) | 0.53 |
| Household crowding index >1# | 233/697 (33.4) | 10/20 (50.0) | 0.12 |
| Children in workplace | 68/705 (9.7) | 3/20 (15.0) | 0.43 |
| Child <5 y in household | 83/712 (11.7) | 4/20 (20.0) | 0.28 |
| Child <18 y in household | 258/712 (36.2) | 13/20 (65.0) | 0.009 |
| Child in household attends day care | 87/699 (12.5) | 6/20 (30.0) | 0.03 |
*Data are no./total (%) unless otherwise specified. A(H1N1)pdm09, pandemic influenza A(H1N1) 2009 virus; IQR, interquartile range. †Participants who did not report any illness or whose nasal swab samples tested negative for influenza. ‡All participants who tested positive were symptomatic. §Participants who had acquired A(H1N1)pdm09 <7 d after vaccination were considered unprotected ¶Defined as biting one’s nails or cuticles or habitually putting one’s fingers in his or her mouth or nose. #Household crowding index is defined as number of persons per household divided by the number of bedrooms.