A search for subclinical infection during a small outbreak of whooping cough: implications for clinical diagnosis.

The transmission of whooping cough in a general practice community was followed after the identification of the first case for nearly three years. Intensive case-finding was undertaken to detect contacts of known cases of whooping cough and to take pernasal swabs from those with any cough; 102 swabs were taken. In three months 39 cases of whooping cough were clinically diagnosed, 17 (44%) of which were confirmed bacteriologically. All had a prolonged paroxysmal cough, one-third reported a catarrhal phase, 18 (46%) vomited with paroxysms and nine (23%) whooped. No isolations of Bordetella pertussis were obtained from the 84 contacts with non-paroxysmal coughs. There was no evidence that subclinical bordetella infection (showing none of the signs of whooping cough) is a common occurrence.It is probable that many recognizable cases of whooping cough are missed because it can be a milder illness than is often realized and commonly exhibits neither whooping, vomiting nor a catarrhal phase. Paroxysms may be infrequent. The diagnosis of whooping cough should be suspected from a prolonged paroxysmal cough alone.