The course of IgA and IgG. The course of IgA (figure 1a) and IgG (figure 1b) levels obtained in all 89 serum samples from the 46 pertussis cases obtained in week 9 and 13 of the pertussis epidemic in the convent population (n = 99). Pertussis cases had a laboratory confirmed B. pertussis infection and a clinical pertussis (see methods). The levels are related to the first day of cough of the pertussis cases. Six serum samples were obtained from cases before they started coughing and 83 samples were obtained from cases who had been coughing for between 1 and 87 days. Lines connect samples obtained from one subject. Dotted lines are from the 5 subjects with a positive culture or PCR.