Volume 11, Number 11—November 2005
Neutralizing Antibody Response and SARS Severity
|OR (95% CI)||p value||Parameter estimates + SE||p value|
|Age (y) (n + 1 vs. n)||0.97 (0.94-1.00)||0.065||0.0056 + 0.0079||0.478|
|Women vs. men||1.24 (0.47-3.3)||0.67||–0.417 + 0.235||0.081|
|Infection source, known vs. unknown||15.6 (5.9-41.4)||<0.0001||0.248 + 0.313||0.431|
|Duration of illness (d) (n+1 vs. n, n = 1 through 44 d)||1.08 (1.025-1.143)||0.004||0.0638 + 0.0233||0.008|
|Time of convalescent-phase serum sample (weeks after fever onset) (n + 1 vs. n, n = 3 through 15 wk)||–||–||0.449 + 0.198||0.026|
|(Duration of illness) ×(Time of convalescent-phase serum sample)||–||–||–0.005 + 0.0024||0.037|
|(Time of convalescent-phase serum sample)2||–||–||–0.025 + 0.012||0.042|
*Logistic model: age, with every additional year of age, the odds of seropositivity is 0.97 (odds ratio, OR) (see Figure 1); sex, the odds for women to be seropositive is 1.24 (OR) when compared with men; infectious source, the odds of patients with known infection source to be seropositive is 15.6 times that of the patients without known source of infection; duration of illness, for every additional day of illness, the odds of seropositivity increases by 1.08.
†Linear mixed model: log2 (neutralizing antibody titer) = β0 + β1 (age) – β1 (sex) + β3 (infection source) + β4 (duration of illness) + β5 (time of convalescent-phase serum sample) –β6 (duration of illness ×time of convalescent-phase serum sample) –β7 (time of convalescent-phase serum sample)2. In results above, the model estimates are based on log2 (titers), to which the time of convalescent-phase serum collection (in weeks postonset of illness, starting from week 3) contributed in 3 terms; the antibody rise follows the first order of weeks postonset, and decay follows the second order of weeks postonset and an interactive term between duration of illness and weeks postonset.