These case definitions, however, have not yet been implemented by all states. For 1987 and 1988, the age-specific incidence rates were similar to those for 1984 and 1985. From 1986 through 1988, as in previous years, infants were at highest risk for pertussis and pertussis-associated complications. Two thirds of the pertussis cases reported during that period in children aged 7 months to 4 years could potentially have been prevented by age-appropriate vaccination.
Diagnostic limitations restrict assessment of the full public health impact of pertussis.
The routinely available methods for laboratory diagnosis of pertussis are culture and DFA testing of nasopharyngeal secretions. Thus, negative culture results may be misleading. DFA testing was performed on nearly three fourths of patients reported to the SPSS, but a positive test did not predict the presence of cough for greater than or equal to 14 days. Thus, clinical criteria may be especially useful when cultures are not obtained or when culture results are negative. With such reporting practices, many patients meeting the CSTE case definitions may go unreported if laboratory tests are negative or not done.