A series of studies of pertussis outbreaks in strictly rural areas included semi-weekly cough plates on all susceptible children and on a selected group of other children and adults comprising about J of the population. Cultures were isolated on Bordet-Gengou agar and confirmed by studies on chocolate agar and by stained smears. 2,000 plates from all sources showed 1.4% positive. Those from cases of the disease showed 6.4% positive. 1 positive plate was discovered prior to development of prodromal symptoms. Plates collected during the 1st wk. of disease showed 43.7% positive, 2nd wk. 39.1%, 3rd wk. 17.4%, 4th wk. 3.5%, and no positives were obtained thereafter. Of the cases furnishing plates, 93% were positive at some time during the course. Number of colonies on individual plates was not correlated with stage of disease. In 5 of 16 cases, a positive report was rendered before clinical symptoms were decisive. 4 individuals not developing the disease showed positive plates; they were classed as carriers. A total of 820 plates was obtained from the general population; 434 were associated with respiratory symptoms. No positive plates were obtained from any of these persons, indicating that few if any of the respiratory symptoms occurring in the community were subclinical pertussis. Pertussis plates, therefore, have a place in a public-health-laboratory program as a means of diagnosis. They are of little use in control of the disease or as a means of quarantine release. The research value is important as a means of increasing knowledge of the epidemiology of the disease.
