What are the steps for a pertussis (whooping cough) workup?

Pertussis Workup: Diagnostic Approach

The workup for pertussis should focus on identifying key clinical characteristics and confirming with appropriate laboratory testing, with PCR testing being the preferred diagnostic method for suspected cases.

Clinical Assessment

Adults

• For adults with acute (<3 weeks) or subacute (3-8 weeks) cough, assess for four key characteristics: paroxysmal cough, posttussive vomiting, inspiratory whooping, and absence of fever 1
• Pertussis is unlikely if the patient has fever or if the cough is not paroxysmal in nature 1
• Pertussis is likely if there is posttussive vomiting or inspiratory whooping sound 1
• Paroxysmal cough has high sensitivity (93.2%) but low specificity (20.6%) for pertussis 1, 2
• Posttussive vomiting and whooping have high specificity (77.7% and 79.5% respectively) but low sensitivity 1, 2

Children

• For children with acute cough (<4 weeks), specifically assess for the three classical characteristics: paroxysmal cough, posttussive vomiting, and inspiratory whooping 1
• Consider pertussis if there is posttussive vomiting, which has moderate sensitivity (60.0%) and specificity (66.0%) 1, 3
• Consider pertussis if there is paroxysmal cough or inspiratory whooping 1, 3

Laboratory Confirmation

• Polymerase chain reaction (PCR) testing of nasopharyngeal specimens is the preferred confirmatory test 4, 5
• Other laboratory methods include:
  • Culture (100% specific) - traditional gold standard but less sensitive than PCR 1
  • Serology (72%-100% specific) 1, 6
  • Oral fluid testing (91%-99% specific) 1

Treatment Approach

• Initiate macrolide antibiotics (preferably azithromycin) when pertussis is suspected to prevent transmission, even though it may not alter the clinical course if started late 3, 4
• For confirmed pertussis, erythromycin is effective in eliminating the organism from the nasopharynx, rendering patients non-infectious 7
• For children, the recommended dosage is 40-50 mg/kg/day of erythromycin in divided doses for 5-14 days 7
• For adults, the usual dosage is 500 mg erythromycin four times daily 7, 8

Special Considerations

• Patients are infectious for approximately three weeks from cough onset 5
• Antibiotic prophylaxis is recommended for household contacts and those at high risk of severe illness 4
• Complications vary by age, with infants more likely to experience severe complications such as apnea, pneumonia, seizures, or death 8
• In adults and adolescents, complications typically result from chronic cough 8

Common Pitfalls to Avoid

• Failing to consider pertussis in patients with prolonged cough, especially if paroxysmal 1, 2
• Waiting for laboratory confirmation before initiating treatment, which may delay prevention of transmission 1, 4
• Missing the diagnosis in adults who may not present with the classic "whoop" 4, 5
• Not providing prophylaxis to close contacts, especially those at high risk 4
• Expecting antibiotics to shorten the disease course or improve symptoms when initiated late in the illness 4, 8