成人百日咳並不少見

NEJM TEACHING TOPIC
A 73-year-old man presented to the emergency department with a 4-day history of nonproductive cough that worsened at night. He did not have fever, chills, headache, myalgias, rhinorrhea, nasal congestion, sore throat, hemoptysis, chest pain, or dyspnea. What is the differential diagnosis?

Cough: Differential Diagnosis
The most common causes of acute cough (lasting <3>8 weeks) is most often attributable to gastroesophageal reflux disease, asthma, the upper-airway cough syndrome (formerly called postnasal drip), cigarette smoking, or use of ACE inhibitors. Other causes of cough include congestive heart failure, irritation of the bronchial airway by a foreign body, and cancer.

Pertussis in Adults
An important, but often overlooked, cause of cough in adults is infection with B. pertussis. Pertussis is often considered a childhood infection; however, several recent studies have shown that it is the cause of 12 to 32% of cases of prolonged cough (lasting >2 to 3 weeks) in adolescents and adults. Childhood vaccination against B. pertussis does not confer lifelong immunity. Immunity wanes after 5 to 10 years and rarely lasts more than 12 years.

Questions
Q : If you suspect pertussis infection in an adult patient, what tests should you perform to confirm the diagnosis?
A: Current recommendations for laboratory testing for pertussis include posterior nasopharyngeal culture or the PCR assay to be used as confirmatory tests for diagnosis. Since B. pertussis preferentially resides in ciliated respiratory epithelium, clinicians must obtain specimens from the posterior nasopharynx, not the anterior nares or throat. The sensitivity of the culture will be reduced by delayed transport to the laboratory and delayed plating of the specimen, as well as previous vaccination, recent antibiotic use, and prolonged illness.

Q: What antibiotic regimens are recommended for the treatment of pertussis? Should you start the antibiotics before the tests results return?
A: Since the results of microbiologic pertussis testing may not be available for a week or more, and because pertussis is highly contagious, antimicrobial treatment should be initiated when testing is ordered. Macrolide therapy is recommended for both treatment and postexposure prophylaxis: for adults, 500 mg of erythromycin four times daily for 14 days; 500 mg of azithromycin on day 1, followed by 250 mg daily on days 2 through 5; or 500 mg of clarithromycin twice daily for 7 days. Antimicrobial treatment initiated after 1 to 2 weeks of symptoms has little effect on the duration of the cough. When pertussis has lasted more than 7 days, antimicrobial therapy has little symptomatic benefit, but it reduces the risk of transmission. Postexposure prophylaxis should be offered to close contacts of patients with laboratory-confirmed cases, regardless of their age or vaccination status.