JSTOR

Methods

A nurse presented to the Occupational Medicine Clinic at Dartmouth‐Hitchcock Medical Center (Lebanon, NH) on July 1, 2003, with a complaint of cough that had lasted 4 weeks. She reported that her adolescent son had been coughing for the previous 6 weeks; he received a diagnosis of viral upper respiratory infection. Cases of pertussis at the son’s school had been documented within the previous months by the state Department of Health and Human Services. A nasal aspirate from the employee was tested for B. pertussis DNA, and results received the following day were positive. The employee was notified and furloughed from work until a 5‐day course of azithromycin therapy was completed.

Employees who worked in or visited the unit where the source case worked were contacted and screened for pertussis symptoms. Employees were asked about work location, schedules, and contacts, both at work and at home (although employee families were not screened). Patients in the unit were also screened for symptoms; recently discharged patients were contacted by phone during a 5‐day period, surveyed for symptoms of pertussis, and tested if symptomatic. If asymptomatic, they were asked to contact the hospital if they developed symptoms of pertussis.

Pertussis cases were defined on the basis of criteria approved by the Centers for Disease Control and Prevention and the Council of State and Territorial Epidemiologists.^6,7 The clinical syndrome is defined as a cough lasting at least 2 weeks with one of the following conditions: paroxysms of coughing, inspiratory whoop, or posttussive vomiting without another apparent cause. Confirmed cases of pertussis met the clinical case definition and were either confirmed by polymerase chain reaction (PCR) analysis or were epidemiologically linked (via direct contact) to a PCR‐confirmed case. Probable cases met the clinical case definition but lacked laboratory confirmation or an apparent epidemiologic link.

Results

The special‐care unit where the source employee worked is designed for treatment of immunocompromised patients who are receiving chemotherapy or undergoing bone marrow transplantation. The unit consists of 8 rooms and a nurses’ station, all of which are separated from the general ward by a glass partition. The rooms are under positive pressure relative to the nurses’ station, and air purity is maintained by high‐efficiency particulate air filters in each room. The nurses’ station is centrally located within the unit and is itself under positive air pressure relative to the remainder of the ward. Staff typically congregate in this central area when not involved in direct patient care. The engineering department reported no problems with the airflow or filtering systems during June 2003.

Of 117 employees screened, 45 (38%) described symptoms and were tested for pertussis by PCR of nasopharyngeal aspirate. Of 44 patients treated in the unit in the 4 weeks before discovery of the first employee case, none reported symptoms consistent with pertussis, and none were tested.

Ten (8.5%) of 117 screened employees met criteria for confirmed pertussis. Including the source employee, 5 employees had a nasal aspirate that was positive for B. pertussis by PCR (Figure). Five additional employee cases were epidemiologically linked to an employee with a PCR‐confirmed case via direct contact within the unit (Table). No probable cases were identified. The mean age of the employees with pertussis was 41 years (range, 33‐54 years). Six of the affected employees were nurses who worked exclusively in the unit, and the other 4 had significant exposure to the unit. Of the 117 exposed employees, 92 received antibiotics as prophylaxis or treatment. The remainder elected to forego antibiotic therapy unless they became symptomatic, and no employees were furloughed unless they were identified as having pertussis.

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Figure.  Onset dates of pertussis symptoms for employees in a hematology‐oncology care unit

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Table.  Demographic and Clinical Characteristics of Employees in a Hematology‐Oncology Care Unit Who Received a Diagnosis of Pertussis

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Discussion

This outbreak demonstrates the transmissibility of B. pertussis in a high‐risk healthcare setting and the current limitations for preventing such outbreaks among nonimmune adults. A pertussis outbreak in a neonatal intensive care unit could have greater consequences if spread to patients. Infants with pertussis are more likely than adults to experience pneumonia (11.6% vs 2.2%), seizures (1.4% vs 0.4%), or death (0.8% vs <0.1%).³ Dependence on clinical recognition of pertussis among healthcare workers is likely to be ineffective as a prevention strategy. It is estimated that only 10% of pertussis cases are reported,^8,9 in part because symptoms may be nonspecific in adults.¹⁰ Indeed, in this outbreak, pertussis was undiagnosed in the index case, who was working symptomatically for 4 weeks despite recognized exposure to a community outbreak.

Since the development of acellular pertussis vaccines, boosting of immunity in adults continues to gain acceptance. Both monocomponent and combination acellular vaccines have been studied for use in adults. Combination vaccines, such as diphtheria‐tetanus toxoids‐acellular pertussis and reduced antigen diphtheria‐tetanus‐acellular pertussis, have shown immunogenicity towards B. pertussis that is equivalent to that of monocomponent acellular pertussis vaccine.^11,12 These combined vaccines offer the additional benefit of boosting immunity to diphtheria and tetanus, with a similar tolerability and adverse‐effect profile to that of the existing tetanus‐diphtheria booster.¹³ It remains unknown, however, whether acellular pertussis vaccine will reduce the community incidence of pertussis. In addition, the duration of immunity conferred by the pertussis booster in adults has not been firmly established.

Although prevention of pertussis among adults is desirable, the true benefit of adult vaccination lies in preventing transmission to infants, who experience the highest mortality. In 2001, the International Consensus Group on Pertussis Immunization called for the establishment of formal recommendations for adolescent and adult immunizations, although the group stopped short of making these recommendations, citing the need for more research. The consensus statement identified several target groups for immunization, including hospital workers.¹⁴ In addition, Canadian guidelines on reimmunization were altered in 2003 to include a dose of diphtheria‐tetanus toxoids‐acellular pertussis vaccine for adults and adolescents, rather than the previously recommended tetanus‐diphtheria booster.¹⁵

A pertussis booster vaccination strategy could be implemented using existing organizational resources and incorporated into existing hospital infection control programs. Vaccination would likely start with new employees and those in high‐risk settings, such as intensive care nurseries. Other employees could be vaccinated at the time of routine injections (eg, influenza vaccination and purified protein derivative placement). Healthcare workers should also be educated about the lack of lifelong immunity to pertussis despite receipt of vaccine during childhood.

It is of interest that no cases were found among the hematology‐oncology unit patients. It is hypothesized that routine careful attention to handwashing and the routine use of protective masks by employees with upper respiratory infections entering patient rooms were protective for the patients. Antibiotic use for other purposes in these patients may have provided protection, but only 13 of 44 patients were treated with antibiotics with known or purported activity against B. pertussis.¹⁶ It was hypothesized that positive air‐pressure rooms provided an additional protective effects, but this could not be assessed. Although employees routinely washed their hands and used masks within patient rooms, they did not use masks within the nurses’ station, leading to transmission during contact within the unit.

Pertussis outbreaks among hospital workers are associated with significant and potentially disastrous complications for patients. There is now a safe and effective vaccine that could potentially prevent transmission within healthcare settings. Although additional study is needed, immunization of hospital workers against pertussis is a logical next step for controlling this disease.