Multivariable Poisson model examining the association between serum IgA ≤70 mg/dL and courses of antibiotic treatment after 1 January /2007*
| Variable | Rate ratio | 95% CI | P value |
| IgA ≤70 mg/dL | 1.90 | 1.24 to 2.90 | 0.003 |
| Age | 0.99 | 0.97 to 1.02 | 0.63 |
| Ever smoker | 0.68 | 0.41 to 1.12 | 0.13 |
*n=914; also adjusted for race, WTC exposure and BMI.
BMI, body mass index; WTC, World Trade Center.