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Pertussis Outbreak Among Adults at an Oil Refinery --- Illinois, August--October 2002
On September 16, 2002, the Crawford County Health Department (CCHD) reported to the Illinois Department of Public Health (IDPH) four cases of cough illness among workers at an oil refinery (total worker population: 750) in Crawford County, Illinois. On August 14, a worker aged 39 years reported to the plant's health unit with a cough lasting 14 days. On the same day, the worker's supervisor aged 50 years visited the health unit for a paroxysmal cough of 3 days' duration and an incident of cough syncope. Both patients were referred to private health-care providers; blood samples from both patients had serologic test results suggestive of recent Bordetella pertussis infection, and CCHD was contacted. On September 18, IDPH and CCHD initiated active surveillance and case investigations. This report summarizes the results of that investigation, which found that during August 1--October 9, pertussis was diagnosed in 15 (10%) of 150 oil refinery workers from two separate operations (n=95) and maintenance (n=55) complexes, who were linked by contact with the ill supervisor. Through enhanced case finding, 24 cases of pertussis, 21 (88%) of which occurred in adults aged >20 years, were identified in this outbreak, underscoring the need to recognize this highly infectious disease in adults and to improve national diagnostic and preventive strategies.
A clinical case was defined as an acute cough illness lasting >2 weeks in a person with 1) at least one of the following: paroxysms of coughing, inspiratory "whoop," or post-tussive vomiting, without other apparent cause or 2) >14 days of cough in a person in an outbreak setting. A confirmed case was defined as a cough illness of any duration in a person with isolation by culture of B. pertussis or a case that met the clinical case definition and was confirmed by polymerase chain reaction (PCR) for B. pertussis DNA or by epidemiologic linkage to a laboratory-confirmed case. A probable case met the clinical case definition, was not laboratory-confirmed, and was not linked by direct contact with a laboratory-confirmed case. At the oil refinery, any worker reporting a cough illness to the health unit was referred to the local community hospital for evaluation for pertussis and interviewed by CCHD or IDPH staff to establish onset of illness, symptoms, area of work and work schedules, and information on all close contacts. Community cases were identified through standard IDPH case report forms submitted by health-care providers to CCHD for suspected cases of pertussis and then reviewed by the IDPH immunization section to determine if the case definition was met.
As of December 13, a total of 17 cases of pertussis have been associated with the oil refinery: four confirmed cases (including one culture-positive case, one PCR-positive case, and two epidemiologically linked cases) and 13 probable cases; 10 patients were males. A pulsed-field gel electrophoresis (PFGE) DNA fingerprint from the B. pertussis isolate from the culture-confirmed case (illness onset date: September 10) was PFGE profile 13. The median age of patients was 40 years (range: 16--53 years). Six patients worked in the same work unit. Eight of 14 patients tested by a private diagnostic laboratory had serologic testing results (anti-B. pertussis IgA, IgM, or IgG enzyme immunoassay) suggestive of recent B. pertussis infection. In addition to the 17 patients identified from the oil refinery, seven patients in the community who were unrelated epidemiologically to the oil refinery also were identified as having probable cases of pertussis; four were males with a median age of 24 years (range: 5--33 years). All 24 patients (Figure) received treatment with macrolide antibiotics and were encouraged to be tested for pertussis by PCR and nasopharyngeal culture. On September 19, with the cooperation of the oil refinery management, 150 close work contacts of the 17 patients at the oil refinery plant were prescribed azithromycin prophylaxis at a dose schedule of 500 mg for the first day, followed by 250 mg daily for the next 4 days.
Other than a meeting lasting approximately 5 minutes conducted indoors each morning, daily work assignments at the plant are performed outdoors. However, workers may congregate in an indoor dining area reserved for lunch.
No cases of pertussis at the oil refinery have been reported since October 9. School officials and health-care providers within the community have been given guidelines on pertussis case recognition, reporting, and prophylaxis measures. IDPH and the local health department continue to perform ongoing case ascertainment.
Reported by: P Skaggs, Crawford County Health Dept, Robinson, Illinois; C Jennings, K Hunt, K McFadden, MS Dworkin, MD, Div of Infectious Diseases, Illinois Dept of Public Health. MJ Parker, E Linder, MD, Marathon Ashland Petroleum Company, Finley, Ohio. KM Bisgard, DVM, Epidemiology and Surveillance Div, National Immunization Program; G Huhn, MD, EIS Officer, CDC.
Among the diseases for which universal childhood vaccination is recommended in the United States, only pertussis has increased in incidence in the United States during the preceding 20 years, from 1,730 cases in 1980 to 8,296 cases provisionally reported in 2002 (1; CDC, unpublished data, 2002). The outbreak described in this report reflects the changing demographics of pertussis in the United States, with reported incidence rates in adults increasing 400% during 1990--2001 (2; CDC, unpublished data, 2002). Adults and adolescents might be a reservoir for B. pertussis in the community because immunity from childhood vaccination declines beginning 5--15 years after the last pertussis vaccine dose (3). Despite increasing recognition of pertussis as a disease affecting older children and adults, pertussis often is overlooked in the differential diagnosis of cough illness in this population (4). Pertussis can be highly infectious during the 3 weeks after illness onset, and infection can spread to exposed infants, who have the highest rates for complications and death (5) (Box. In this outbreak, pertussis was not considered initially in the index patient's 14-day cough illness until the patient's supervisor reported to the oil refinery health unit concurrently with cough syncope, triggering referral of both patients to the local community hospital for evaluation for pertussis. Emblematic in this outbreak was the protracted duration of cough symptoms in the first patient, followed by a comprehensive public health response once several close contacts became infected and, late in the outbreak, B. pertussis was cultured successfully from an oil refinery worker; isolation of B. pertussis from an adult is uncommon.
In Illinois, 46 of 191 cases (24%) of reported pertussis in 2001 occurred in adults aged >20 years (incidence rate: 0.5 per 100,000 population), a proportion similar to that of cases in the United States among this age group (1). Persons aged 10--19 years comprised 18% of all cases in 2001 in Illinois. Waning vaccine-induced immunity probably accounts for susceptibility to B. pertussis infection in both adults and adolescents (3,6). Since the 1980s, the reported incidence rates in adolescents and adults in the United States have increased as a result of changes in reporting, a true increase in incidence, or both (1,2). In 1995, the case definition for pertussis was expanded to include PCR-positive tests and epidemiologic linking of pertussis cases as confirmation criteria. In addition, a possible increase in awareness of pertussis in older age groups within the medical community during the 1990s might have contributed to increased diagnosis rates in this population (7).
Adults with pertussis can have mild symptoms and might not seek medical care, and clinicians might not consider pertussis as a cause of illness (8). Although the fastidious B. pertussis bacterium often cannot be isolated, to confirm diagnosis in symptomatic adults, health-care providers should obtain a nasopharyngeal aspirate or swab for B. pertussis culture within 2 weeks of cough onset. In this outbreak, serologic testing for diagnosis of recent B. pertussis infection was performed in the majority of cases. No serologic assay for a single convalescent sera is currently approved or recommended for serodiagnosis of pertussis. Because adults might report to health-care providers late in the disease course, a standardized and valid serologic test is needed to diagnose recent B. pertussis infection in adults (9).
As one of several state health departments with enhanced pertussis surveillance systems, IDPH analyzes B. pertussis isolates from cases by PFGE. The single isolate in this outbreak indicated PFGE profile 13, the most frequently identified pattern from B. pertussis isolates in the United States. Identification of pertussis DNA fingerprints by PFGE might allow health officials to track disease transmission and associated outbreaks.
A 14-day course of erythromycin, a macrolide antibiotic with substantial in vitro and in vivo activity against B. pertussis, is the recommended antimicrobial for treatment of patients with pertussis and for prophylaxis of close contacts. Treatment and prophylaxis are most effective when erythromycin is administered to patients within 3 weeks of illness onset and to close contacts within 3 weeks of cough onset in the primary case (9). During an outbreak, repeated exposure to pertussis might warrant repeated courses of erythromycin. If erythromycin is poorly tolerated because of gastrointestinal side effects, trimethoprim-sulfamethoxazole can be prescribed; azithromycin and clarithromycin might be effective alternatives in the eradication of B. pertussis in symptomatic patients (9,10). However, effectiveness of azithromycin or clarithromycin as prophylaxis for asymptomatic close contacts in an outbreak setting is not well documented.
Outbreaks of pertussis in adults are controlled through prompt treatment of patients and antimicrobial prophylaxis for close contacts. Acellular pertussis vaccines are licensed in the United States for infants and children aged 6 weeks--6 years (i.e., before the seventh birthday). These vaccines might have a future role in the prevention of disease and control of outbreaks in older age groups (4,5,7).
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