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Pertussis, also know as whooping cough, is highly communicable bacterial infection caused by Bordetella pertussis, or occasionally B. parapertussis. Bordetella species are fastidious gram-negative coccobacilli. Transmission occurs through direct contact with discharges from respiratory mucous membranes of an infected person. The incubation period of pertussis is commonly 7-10 days after exposure but may range from 4-21 days. Pertussis is highly communicable, infecting 80-90% of susceptible contacts. Any child, adolescent or adult who is symptomatic or has confirmed pertussis should be excluded from daycare, school or work until they have completed 5 days of a recommended antimicrobial therapy. Symptomatic people who do not take recommended antimicrobial therapy should be excluded until 21 days have elapsed from onset of cough. From the onset of symptoms, the disease can take 6-8 weeks to resolve. Pertussis can cause severe disease in very young children. It begins with mild upper respiratory tract symptoms and progresses to cough, and can further progress to severe paroxysms, often with a characteristic inspiratory whoop followed by vomiting. Fever is absent or minimal. In infants younger than six months, apnea is a common manifestation and whoop may be absent. Pneumonia is the most common complication and cause of pertussis-related deaths. Young infants are at highest risk for pertussis-related complications, including seizures, encephalopathy (swelling of the brain), and otitis media (severe ear infection). There are about 10-15 deaths each year in the United States. Immunity due to either infection or vaccination is not long lasting. Pertussis is thought to be the cause of 12% to 26% of "cough illness" in adults. Adult infections should be suspected when an illness that begins with cold symptoms is prolonged and associated with a non-productive paroxysmal cough that worsens at night. Clinical diagnosis is complicated by the fact that the characteristic cough (whoop) is rarely observed in adults. Although mortality from this disease is low among adolescents and adults, these populations are a potential reservoir for pediatric infections. Pertussis can be very severe in young infants and early diagnosis is essential to limit complications and minimize transmission of the disease. Treatment for pertussis, as well as chemoprophylaxis for exposed persons, usually consists of a prescription of azithromycin, erythromycin, clarithromycin, or trimethoprim-sulfamethoxazole. Exposure is defined as face-to-face contact, direct contact with respiratory, oral, or nasal secretions, or being in the same room or ward with a coughing pertussis case-patient. Immunization against pertussis with DTaP vaccine is recommended by both the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) and should be administered in 5 doses: at 2, 4, 6, and 15-18 months of age and 4 - 6 years of age. The vaccine is not given to people 7 years of age and older. Making a specific diagnosis of pertussis in patients with clinical evidence of infection can be challenging. All suspected cases of pertussis should have a nasopharyngeal aspirate or swab obtained from the posterior nasopharynx. Throat and anterior nasal swabs are insufficient for the recovery of B. pertussis. Because of the low yield of direct smears and cultures for the organism, PCR has become the preferred method for diagnosis of acute disease. The sensitivities for detection of the organism from respiratory specimens are reportedly as follows: culture, 15%; DFA, 52%; PCR, 93%. The PCR assay detects both B. pertussis and B. parapertussis. Bordetella serology is both sensitive and specific, and is a reasonable alternative to diagnosis when collection of a nasopharyngeal specimen is not possible. However, diagnosis by serology generally requires the comparison of acute and convalescent samples collected over a 4-week period. The presence of Bordetella-specific IgM antibody in a single specimen can indicate acute disease, but may persist for up to 6 months after infection. IgG antibodies are only of use in active infection when a rise in antibody level is seen in paired sera. A significant rise may not always be demonstrated as peak levels of IgG may be reached before the first sample is collected. Specific IgG is also useful to assess immune response to vaccine, or evaluate prior exposure to the organism. IgA does not appear to contribute significantly to the diagnostic sensitivity of paired sera for acute infection. In summary, the test of choice for the diagnosis of pertussis is PCR from a nasopharyngeal specimen. Special transport media and swabs are necessary. Serologic testing requires one serum gel tube. |
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