How long after onset of Pertussis (whooping cough) do antibodies become detectable?

From the Guidelines

Pertussis antibody testing typically becomes reliable 2-3 weeks after symptom onset, as indicated by the most recent and highest quality study 1. In the early stages of whooping cough (pertussis), antibody tests may produce false negative results because the body hasn't yet produced sufficient antibodies against Bordetella pertussis.

Key Points to Consider

• The body requires time to recognize the pathogen and mount a specific antibody response, which is why serologic testing for pertussis-specific antibodies becomes more useful for diagnosis after the initial period of illness.
• PCR testing of nasopharyngeal specimens is preferred during the first 3-4 weeks of illness, as it can detect the bacterial DNA directly, as noted in 1.
• The antibody response continues to increase for several weeks, with peak levels usually occurring 4-8 weeks after infection.

Clinical Implications

• If pertussis is suspected clinically, treatment with macrolide antibiotics should be initiated promptly without waiting for test results, especially in the early catarrhal stage when treatment is most effective at reducing symptoms and contagiousness, as recommended in 1.
• The decision to treat with antibiotics is frequently based on a clinical diagnosis rather than waiting for laboratory confirmation, highlighting the importance of prompt treatment in preventing the spread of the disease.

Diagnostic Approach

• A combination of clinical judgment and laboratory testing, including PCR and serology, is essential for making an accurate diagnosis of pertussis.
• The most recent study 1 provides guidance on the clinical diagnosis of pertussis-associated cough in adults and children, emphasizing the importance of considering both clinical and laboratory findings in making a diagnosis.

From the Research

Antibody Detection in Pertussis

• Antibodies against pertussis can be detected through various methods, including enzyme immunoassay (EIA) 2.
• The detection of antibodies depends on the type of antibody and the stage of the disease. For example, IgM antibodies are typically detected early in the disease, while IgG and IgA antibodies are detected later 2, 3.

Timing of Antibody Detection

• Increased levels of IgM antibodies can be detected predominantly from week 1 to 5 after the onset of the disease 2.
• IgA and IgG antibodies can be detected from week 1 to 3 after the onset of the disease, with 67% and 78% of patients having increased levels, respectively 2.
• The combination of IgA, IgG, and IgM antibody levels is the most effective approach for serological diagnostics of pertussis due to the heterogeneity of anti-pertussis antibodies at different stages after the onset of the disease 2.

Sensitivity and Specificity of Antibody Detection

• The sensitivity and specificity of single IgA and IgG levels for early diagnosis of pertussis in adults have been assessed, with levels of 24 U/ml for IgA and 27 U/ml for IgG giving sensitivities of 100% and 75%, respectively, in the first 2 weeks 3.
• The specificity of IgA and IgG levels was 82% and 89%, respectively, in internal controls, and 90% in external controls 3.
• The diagnostic utility of in-house anti-PT IgG and anti-PT IgA assays has been evaluated prospectively in an Australian community-based cohort, with both assays having good specificity, but anti-PT IgG assay being consistently more sensitive than anti-PT IgA assay 4.