D-093. Serologic Correlates of Immunity to Bordetella pertussis Cough Illness

H. Hallander¹, J. D. Cherry², L. Gustafsson¹, J. Storsaeter³, U. Heininger⁴;
¹Swedish Inst. for Infectious Disease Control, Solna, SWEDEN, ²David Geffen Sch. of Med. at Univ. of California, Los Angeles, CA, ³GlaxoSmithKline, Solna, SWEDEN, ⁴Univ. Children's Hosp., Basel, SWITZERLAND.

Background: It is generally stated that no serologic correlates of immunity to pertussis have been established. However in two separate household contact studies we have previously presented data indicating that low levels of antibody to pertactin (PRN) and fimbriae (FIM) and high levels to pertussis toxin (PT) offered considerable protection. (Vaccine 1998; 16:1907-1916 and Vaccine 1998; 16:1901-1906) Presently we have done an additional analysis in the Sweden study. Methods: In the Sweden study there were 209 children exposed in the household and of these 149 developed cough illness with documented B pertussis infection and 60 remained well. Using acute-phase sera and sera drawn prior to exposure we examined the role of antibody to PT, FHA, PRN and FIM-2/3 in protection by a classification tree analysis (CART, Salford Systems, 1997). This tree uses the method of binary recursive partioning and looks at all values of all four specific antibodies and first finds a particular value that best separates the cases from the non-cases. This creates two daughter nodes and repeats the procedure in each node. Results: If the antibody value to PRN was > 8.25 EU/ml there was a 74.5% chance of being a non-case whereas if the value was < 8.25 EU/ml there was only a 15.4% chance of being a non-case. If the antibody value to PRN was > 8.25% and the value to FIM-2/3 was > 73.9 EU/ml the chance of being a non-case was 100%. If in the model FIM-2/3 is forced in for the first split of the tree the findings are as follows: If the FIM-2/3 value is > 7.65 EU/ml there is a 66% chance of being a non-case whereas if the value is < 7.65 EU/ml the likelihood of being a non-case is only 14%. If the FIM-2/3 value is > 7.65 EU/ml and the PRN value is > 3.05 EU/ml there is a 73% chance of being a non-case. If the PRN value was > 8.9 EU/ml and the PT value was > 6.5 EU/ml the chance of being a non-case was only 62.96% whereas if the PT value was < 6.5 EU/ml the chance of being a non-case was 90%. Conclusions: The findings in this study suggest that low levels of antibody to PRN and FIM-2/3 are highly protective, that high levels or antibody to FIM add to the PRN protection and that there may be antagonism between PRN (and FIM; data previously shown) and PT antibodies.