KEYWORDS:
Surveillance, Pertussis reporting

BACKGROUND:
In Los Angeles County (LAC), suspected and confirmed pertussis cases must be reported to the health department within one working day. Previous studies have concluded that a substantial number of pertussis cases remain unreported, or are reported late. Delayed reporting can potentially lead to the spread of cases and increased medical costs. It is unclear how successful LAC’s surveillance system is at identifying hospitalized pertussis cases.

OBJECTIVE(S):
To estimate the completeness of hospital pertussis reporting and attempt to identify hospitals that are underreporting.

METHOD(S):
Using 1999 Office of Statewide Health Planning and Development (OSHPD) hospital discharge data, records with an LAC patient residence and a discharge diagnosis of ‘Bordetella pertussis’ or ‘whooping cough, unspecified organism’ were selected. Known duplicate admissions were removed by matching on a unique identifier. Since 63% of the records did not contain this unique identifier, the number of remaining duplicate admissions was estimated by matching variables such as age at admission and partial zip code. The resulting OSHPD records were compared to hospitalized cases reported to the LAC health department during 1999 to determine the extent of pertussis under-reporting.

RESULT(S):
Using OSHPD data, the estimated number of LAC residents with a pertussis discharge diagnosis in 1999 was between 201 and 241. During the same period in LAC, 154 hospitalized pertussis cases were reported to the health department. Therefore, the percentage of hospitalized pertussis cases reported to LAC in 1999 ranged from 64% to 77% of the OSHPD estimate. Reporting varied substantially by hospital.

CONCLUSIONS(S):
Although limited by the inability to accurately identify duplicate admissions, even the most conservative estimate shows substantial pertussis under-reporting. Heightened surveillance may be needed in hospitals with poor reporting.

LEARNING OBJECTIVES:
Reveal the extent of pertussis underreporting from hospitals, and the need for further research on why hospitals are not reporting.