Is pertussis testing necessary in cases of strong suspicion when treatment with azithromycin (Azithromycin) is already planned?

From the Guidelines

Testing for pertussis is necessary even when treatment with azithromycin is already planned, as it helps with public health reporting, contact tracing, and appropriate isolation measures, and ensures appropriate management of the patient and protection of vulnerable contacts. The standard diagnostic test is a nasopharyngeal swab for PCR, which is most accurate early in the illness 1. While empiric treatment with azithromycin (500 mg on day 1, then 250 mg daily for days 2-5) should be started promptly in suspected cases, especially during the catarrhal phase when treatment is most effective, having a confirmed diagnosis ensures that the patient receives the most appropriate treatment and that public health measures can be taken to prevent the spread of the disease. Some key points to consider when testing for pertussis include:

• The importance of early diagnosis and treatment in preventing the spread of the disease and reducing morbidity and mortality
• The use of PCR as the standard diagnostic test, which is highly sensitive and specific 1
• The need for empiric treatment with azithromycin in suspected cases, while awaiting laboratory confirmation
• The importance of laboratory confirmation in guiding treatment and public health measures, and in distinguishing pertussis from other conditions with similar symptoms, such as viral respiratory infections or mycoplasma 1. In terms of treatment, azithromycin is a recommended antibiotic for the treatment of pertussis, and is generally well-tolerated and effective 1. However, it is essential to note that the treatment of pertussis should be guided by laboratory confirmation, and that public health measures should be taken to prevent the spread of the disease. Some of the benefits of testing for pertussis include:
• Improved patient outcomes through targeted treatment and management
• Reduced risk of transmission to vulnerable contacts, such as young infants and older adults
• Enhanced public health surveillance and outbreak detection
• More effective use of antibiotics and reduced risk of antibiotic resistance. Overall, testing for pertussis is a crucial step in the diagnosis and management of the disease, and should be performed even when treatment with azithromycin is already planned.

From the FDA Drug Label

Appropriate culture and susceptibility tests should be performed before treatment to determine the causative organism and its susceptibility to azithromycin. Therapy with azithromycin may be initiated before results of these tests are known; once the results become available, antimicrobial therapy should be adjusted accordingly The answer to whether pertussis testing is necessary in cases of strong suspicion when treatment with azithromycin is already planned is:

• Pertussis is not mentioned in the provided drug label.
• The label does discuss the importance of culture and susceptibility tests to determine the causative organism and its susceptibility to azithromycin.
• It does not provide information on pertussis testing.
• Therefore, no conclusion can be drawn from the provided label regarding pertussis testing 2

From the Research

Pertussis Testing Necessity

• The necessity of pertussis testing in cases of strong suspicion when treatment with azithromycin is already planned can be evaluated based on the available evidence.
• Studies have shown that azithromycin is as effective as erythromycin in treating pertussis, with fewer adverse effects and better adherence to therapy 3, 4.
• A study published in 2004 found that azithromycin had a bacteriologic cure rate of 100% in patients with pertussis, with no bacterial recurrence detected after treatment 4.
• Another study published in 1996 found that short-term treatment with azithromycin was effective in eradicating Bordetella pertussis from the upper respiratory tract of infants and young children 5.
• A prospective, open, noncomparative study published in 1999 found that azithromycin given once daily for 3 or 5 days was effective in eradicating Bordetella pertussis from the upper respiratory tract of infants and young children, with a negative culture rate of 94.3% on day 7 and 100% on day 14 6.

Diagnostic Tests

• Diagnostic tests for pertussis have low sensitivity, and treatment should be based on clinical suspicion rather than test results 3.
• The Centers for Disease Control and Prevention (CDC) recommend that physicians treat clinically suspected pertussis with antimicrobials, regardless of test results.

Treatment

• Azithromycin is a recommended treatment for pertussis, with a shorter course of treatment and fewer adverse effects compared to erythromycin 3, 4.
• The American Academy of Pediatrics recommends azithromycin as a first-line treatment for pertussis in children, with a dose of 10 mg/kg on day 1, followed by 5 mg/kg once daily for 4 days 4.