What conditions can mimic whooping cough (pertussis)?

Conditions That Mimic Whooping Cough (Pertussis)

Several infectious and non-infectious respiratory conditions can present with prolonged paroxysmal cough similar to pertussis, and the CDC emphasizes that these mimics must be systematically excluded when evaluating patients with persistent cough. 1

Primary Infectious Mimics

Other Bordetella Species

• Bordetella parapertussis causes a pertussis-like illness with similar symptoms but typically shorter duration, as it does not produce pertussis toxin (the primary agent responsible for severe coughing). 1
• Bordetella bronchiseptica and Bordetella holmesii are rare causes of whooping cough-like disease. 1

Viral Respiratory Infections

• Adenoviruses can cause prolonged paroxysmal cough that mimics pertussis. 1
• Respiratory syncytial virus (RSV) presents with cough and respiratory symptoms that overlap with pertussis, particularly in infants. 1
• Influenza A and other viral lower respiratory tract infections can mimic acute bronchitis and present with persistent productive cough. 1

Atypical Bacterial Infections

• Mycoplasma pneumoniae is a common mimic that causes prolonged cough illness in adolescents and adults. 1
• Chlamydia pneumoniae (including TWAR strain) can cause acute infectious cough that responds to antibiotic therapy if initiated early. 1

Non-Infectious Respiratory Conditions

Acute Conditions

• Acute asthma can present with paroxysmal cough and wheezing that mimics acute bronchitis or pertussis. 1
• Acute exacerbation of chronic bronchitis presents with increased cough, sputum production, and purulence that can be confused with pertussis. 1
• The common cold with postnasal drip can cause persistent cough, though typically of shorter duration. 1

Chronic/Subacute Conditions

• Postinfectious cough following any upper respiratory tract infection can persist for 3-8 weeks with paroxysmal features, making it difficult to distinguish from pertussis without laboratory confirmation. 1
• Upper airway cough syndrome (UACS) from persistent postnasal drip can cause chronic paroxysmal cough. 1
• Bronchial hyperresponsiveness following viral infections can manifest as persistent paroxysmal cough that mimics pertussis. 1

Key Distinguishing Features to Assess

Clinical Characteristics That Suggest Pertussis Over Mimics

• Paroxysmal cough has 93.2% sensitivity for pertussis—its absence makes pertussis unlikely, though it is present in many mimics (low specificity of 20.6%). 2
• Posttussive vomiting has high specificity (77.7%) for pertussis—when present, it strongly suggests pertussis over other conditions. 2
• Inspiratory whoop has high specificity (79.5%) for pertussis—when present, it strongly distinguishes pertussis from mimics. 2
• Absence of fever helps distinguish pertussis from many infectious mimics, as fever is uncommon in pertussis. 2

Important Caveats

• Previously vaccinated adolescents and adults may have milder illness with absent whoop, making clinical distinction from other respiratory infections extremely difficult. 1, 2
• Infants can present atypically with apneic spells and minimal cough, which can be mistaken for other serious respiratory conditions. 1, 2
• Cough duration exceeding 2 weeks with paroxysms, posttussive vomiting, or inspiratory whoop should trigger consideration of pertussis even when other diagnoses seem more likely. 2

Practical Diagnostic Approach

When to Suspect Pertussis Despite Potential Mimics

• Cough persisting >2 weeks accompanied by paroxysms, posttussive vomiting, or inspiratory whooping sound meets clinical case definition. 2
• Recent pertussis exposure or outbreak in the community should lower threshold for testing. 3
• PCR testing of nasopharyngeal specimens is the preferred confirmatory test to distinguish pertussis from mimics. 2

Common Pitfall to Avoid

• Do not dismiss pertussis based solely on vaccination history, as immunity wanes 5-10 years after the last dose, and breakthrough infections are common. 1, 2
• Do not wait for laboratory confirmation to initiate treatment when pertussis is clinically suspected, as early macrolide therapy prevents transmission even if the diagnosis is later ruled out. 2