Sampling method

In the current study, the sample size was estimated to provide 80% statistical power based on a prevalence rate of 0.47 for pertussis,[10] 2.5% allowed error, 95% z score using the formula: n = z² × p (1 − p)/d². Finally, 1530 samples were determined. To compensate for probably loss of serums during lab procedure, 1593 samples were included in the study. The samples were selected by random simple sampling method from the serum and information bank and transported to Infectious Diseases and Tropical Medicine Research Center, Isfahan University of medical sciences during 1 h, under refrigerated conditions. Subjects were eliminated from the analysis if they did not have the serum sample volume required for analysis and if information was missing.