TABLE 1.
Demographic, clinical, and virologic characteristics of the study population
| Characteristic | Values for young children (aged <5 yr)a |
Values for elderly patients (aged ≥75 yr) |
||||
|---|---|---|---|---|---|---|
| Case (n = 32) | Control (n = 18) | P value | Case (n = 25) | Control (n = 25) | P valuea | |
| Age (mean ± SD) (yr) | 3.0 ± 0.9 | 3.0 ± 1.0 | NS | 83.6 ± 6.3 | 82.5 ± 6.2 | NS |
| Male gender (n [%]) | 15 (47) | 7 (39) | NS | 12 (48) | 13 (52) | NS |
| Illness onset-to-presentation interval (median [IQR]) (days) | 3.5 (2.0–6.0) | 3.0 (1.5–4.0) | NS | 1.0 (1.0–2.0) | 1.0 (1.0–2.5) | NS |
| Virus subtype (n [%]) | ||||||
| Influenza A | 13 (41) | 12 (48) | ||||
| H1N1 | 1 (3) | 0 (0) | ||||
| H3N2 | 12 (38) | 12 (48) | ||||
| Influenza B | 19 (59) | 13 (52) | ||||
| Comorbidity (n [%]) | 0 (0) | 0 (0) | 20 (80) | 17 (68) | NS | |
| Pneumonia (n [%]) | 0 (0) | 3 (17) | <0.05 | 8 (32) | 10 (40) | NS |
a
Cases and controls were defined using RT-PCR assays as references. There were 7 influenza cases of young children who initially tested negative by immunofluorescence assay and later positive by RT-PCR assays for influenza B. The estimated sensitivity of the immunofluorescence assay was 88% for all influenza cases (with reference to RT-PCR assay). NS, not significant.