Table 2.
Pre-season HI titer detection and effect on homosubtypic infection.
| Season | Infecting/serology strain | Pre-season HI titer | n infected/n with titer (%) | OR for each 2-fold titer increase [95% CI] | OR for each 2-fold titer increase, adjusted for age [95% CI] |
|---|---|---|---|---|---|
| 1 | H1N1 | <=10 | 35/486 (7.2) | 0.95 [0.63–1.43]; | 0.86 [0.54–1.36]; |
| A/Brisbane/59/2007-like | 20 | 3/36 (8.3) | p = 0.79 | p = 0.52 | |
| 40 | 2/21 (9.5) | ||||
| 80 | 0/5 (0.0) | ||||
| 1 | H3N2 | <=10 | 9/359 (2.5) | 0.91 [0.71–1.17]; | 0.75 [0.48–1.16]; |
| A/Brisbane/10/2007-like | 20 | 1/73 (1.4) | p = 0.45 | p = 0.19 | |
| 40 | 2/56 (3.6) | ||||
| ≥80 | 0/60 (0.0) | ||||
| 1 | B/Florida/04/2006-like | <=10 | 53/285 (18.6) | 0.65 [0.53–0.79]; | 0.65 [0.54–0.80]; |
| 20 | 8/121 (6.6) | p < 0.0001 | p < 0.0001 | ||
| 40 | 8/67 (11.9) | ||||
| ≥80 | 1/75 (1.3) | ||||
| 2 | H1N1 | <=10 | 38/410 (9.3) | 1.10 [0.89–1.36]; | 0.90 [0.71–1.15]; |
| A/Brisbane/59/2007-like | 20 | 7/51 (13.7) | p = 0.39* | p = 0.40* | |
| 40 | 2/19 (10.5) | ||||
| ≥80 | 0/14 (0.0) | ||||
| 2 | H3N2 | <=10 | 67/404 (16.6) | 0.69 (0.52–0.90); | 0.61 [0.44–0.84]; |
| A/Perth/16/2009-like | 20 | 2/48 (4.2) | p = 0.008 | p = 0.002 | |
| 40 | 2/23 (8.7) | ||||
| ≥80 | 0/19 (0.0) | ||||
| 2 | B/Florida/04/2006-like | <=10 | 47/302 (15.6) | 0.79 [0.65–0.97]; | 0.78 [0.63–0.97]; |
| 20 | 6/93 (6.5) | p = 0.03 | p = 0.02 | ||
| 40 | 4/73 (5.5) | ||||
| ≥80 | 2/26 (7.7) | ||||
| 3 | H1N1 | <=10 | 103/526 (19.6) | 0.54 [0.27–1.10]; | 0.77 [0.40–1.49]; |
| A/California/04/09-like | ≥20 | 1/14 (7.1) | p = 0.09 | p = 0.43 |
Note that titers are modeled as a continuous variable and do not use the categorization shown, therefore 0 values in a category do not prevent analysis.
*/** Test for non-linear (quadratic) effect of (log2-) titer on outcome: p < 0.05 (*).
Between-strain comparisons of titer effects on the risk of infection (not adjusted for age):
- H1 vs. H3: p = 0.07 (using data from all 3 seasons) [p = 0.87 (season 1), p = 0.008 (season 2)].
- H1 vs. B: p = 0.003 (using data from all 3 seasons) [p = 0.10 (season 1), p = 0.03 (season 2)].
Between-strain comparisons of titer effects on the risk of infection (adjusted for age):
- H1 vs. H3: p = 0.03 (using data from all 3 seasons) [p = 0.82 (season 1), p = 0.006 (season 2)].
- H1 vs. B: p = 0.02 (using data from all 3 seasons) [p = 0.18 (season 1), p = 0.09 (season 2)].