KEYWORD1:
Bordetella pertussis, pertussis, serology, immunogenic

BACKGROUND:
As of November 21, 2002 157 cases of pertussis have been reported in Illinois. 67 (42.67%) have occurred among adults age 20 plus. We report a pertussis outbreak among adult employees at an oil refinery in Illinois through October 15, 2002. Pertussis is the only vaccine preventable disease that has experienced an increase in incidence in the US in the past 20 years.

OBJECTIVE:
As widespread childhood vaccination confers temporary immunity, adults are the major carriers of Bordetella pertussis. Pertussis is often overlooked in the differential diagnosis of cough illness in this population, despite the awareness of this disease as affecting older children and adults. This outbreak highlights the emerging problem of pertussis infection in adults.

METHOD:
On September 16, 2002 we learned of 4 employees with symptoms compatible with pertussis. Active surveillance and case investigation began. Positive serology was not considered for confirmation. Seventeen cases have been associated with the oil refinery: four confirmed and 13 probable cases. Age range of cases was 16 - 52 years. Eight cases with serology were interpreted as positive. Seven cases occurred in the community.

RESULT:
With cooperation of management, 150 contacts were given azithromycin prophylaxis. With aggressive investigations and education of health care providers this outbreak was contained by October 30, 2002. Complicating this investigation was the arrival of 1,500 new contract employees at the plant on October 7, 2002.

CONCLUSION:
The oil refinery is primarily an outdoor facility, but spread of disease still occurred. Diagnosis of pertussis in adults is a challenge for several reasons. Adults may not seek medical care, and may have mild symptoms. Obtaining positive cultures in adults is difficult, and currently there is not an accepted standard for a single serological specimen.
LEARNINGOBJECTIVES:
Case definition revisions.
Standardize serological testing.
Immunogenic vaccines for adults.