Overview
Definition:
Post-exposure prophylaxis (PEP) for pertussis involves administering antibiotics to close contacts of a confirmed or suspected case to prevent secondary transmission and reduce the risk of developing the disease
It is particularly crucial for individuals at high risk of severe complications, including infants, pregnant women, and immunocompromised individuals.
Epidemiology:
Pertussis remains a significant public health concern globally, with endemic cycles and periodic outbreaks
While vaccination significantly reduces incidence, waning immunity and gaps in vaccine coverage contribute to its resurgence
Infants under one year are at highest risk for severe illness, hospitalization, and death
Household contacts are the most common source of infant infection.
Clinical Significance:
Early identification and prompt PEP for household contacts are critical for controlling pertussis outbreaks, especially in preventing severe disease and mortality in vulnerable populations like infants
This strategy is a cornerstone of pediatric infectious disease management and is frequently tested in postgraduate examinations.
Clinical Presentation Of Pertussis
Symptoms:
Early catarrhal stage (1-2 weeks): Mild cough, rhinorrhea, low-grade fever, conjunctivitis
Paroxysmal stage (2-6 weeks): Characteristic inspiratory "whoop" after coughing fits, followed by expulsion of thick mucus
Post-tussive vomiting and cyanosis can occur
Convalescent stage (weeks to months): Gradual resolution of cough, with lingering paroxysms.
Signs:
In infants: Apnea, seizures, pneumonia, encephalopathy, failure to thrive
In older children and adults: Persistent cough, often without a significant "whoop," may be mistaken for prolonged viral bronchitis.
Diagnostic Criteria:
Clinical diagnosis based on characteristic cough paroxysms, especially in unvaccinated or incompletely vaccinated individuals
Laboratory confirmation is essential for definitive diagnosis and public health surveillance, including PCR testing of nasopharyngeal secretions and serology.
Diagnostic Approach For Contacts
History Taking:
Detailed history of the index case, including symptom onset, duration, and treatment
Ascertain vaccination status of the contact (child and adult), including dates and types of vaccines received
Identify any underlying medical conditions in the contact that may increase their risk of severe pertussis.
Physical Examination:
Assess for signs of respiratory distress, including tachypnea, retractions, and grunting
Auscultate lungs for adventitious sounds
In infants, monitor for apnea and cyanosis
Perform a thorough general examination to rule out other causes of respiratory symptoms.
Investigations For Contacts:
Diagnostic confirmation of the index case is paramount
For symptomatic contacts, consider nasopharyngeal swab for PCR testing for *Bordetella pertussis*
Serology (anti-pertussis toxin IgG) can be useful for confirming infection retrospectively in individuals with a prolonged cough illness, but is not typically used for acute diagnosis in contacts.
Differential Diagnosis For Contacts:
For asymptomatic household contacts, the primary concern is preventing transmission
If a contact develops symptoms, differentials include common viral upper respiratory infections, bronchitis, pneumonia, and other causes of cough such as asthma or foreign body aspiration.
Management Of Contacts
Indications For Prophylaxis:
PEP should be offered to all household contacts of a confirmed or highly suspected case of pertussis, regardless of age or vaccination status, especially if the index case onset was within 3 weeks
Particular emphasis should be placed on close contacts such as infants, pregnant women (especially those in their third trimester), and individuals in close contact with infants.
Pharmacological Prophylaxis:
The preferred agents are macrolides due to their efficacy and ability to eradicate nasopharyngeal carriage
Empiric treatment should be initiated promptly
- Azithromycin: 10 mg/kg once daily for 5 days (maximum 500 mg/day for adults)
For infants < 6 months, 5 mg/kg twice daily for 5 days
- Clarithromycin: 7.5 mg/kg twice daily for 7 days (maximum 500 mg twice daily for adults)
- Erythromycin: 12.5 mg/kg twice daily for 14 days (maximum 500 mg four times daily for adults)
Erythromycin is generally less well-tolerated and has more drug interactions than azithromycin.
Alternative Regimens:
For individuals with contraindications to macrolides, trimethoprim-sulfamethoxazole (TMP-SMX) can be considered.
- TMP-SMX: 8 mg/kg/day of TMP component divided into two doses for 14 days (maximum 160 mg TMP/800 mg SMX twice daily for adults).
Supportive Care For Prophylaxis:
Educate household members about the signs and symptoms of pertussis, emphasizing the importance of seeking medical attention if symptoms develop
Advise on measures to prevent further transmission, such as respiratory hygiene
Ensure all eligible individuals are up-to-date with their pertussis-containing vaccine series, including boosters.
Vaccination In Contacts
Infants And Children:
Infants should receive their primary DTaP (diphtheria, tetanus, acellular pertussis) series starting at 2 months of age
If an infant is exposed and has received fewer than 3 doses, they should complete the primary series as soon as possible
Consider early vaccination (from 6 weeks) if there is high risk of exposure and no contraindications
Tdap booster doses are recommended for adolescents and adults.
Pregnant Women:
Administer Tdap vaccine during each pregnancy, ideally between 27 and 36 weeks of gestation, to provide passive immunity to the infant
This is a critical strategy to protect newborns from pertussis.
Adults And Adolescents:
Individuals who have not received a Tdap vaccine should receive a dose
Adults who have close contact with infants should receive a Tdap booster if they have not received one in the past 10 years.
Updated Vaccination Status:
Ensure all family members have received age-appropriate pertussis vaccinations and boosters
Waning immunity is a concern, and updated vaccination status can significantly reduce the risk of acquiring and transmitting pertussis.
Complications And Prevention In Contacts
Potential Complications In Contacts:
While PEP aims to prevent illness, if infection occurs despite prophylaxis, contacts may still develop complications including pneumonia, otitis media, syncope, and in rare cases, encephalopathy or hemorrhage
Infants remain at highest risk for severe outcomes.
Prevention Of Secondary Transmission:
PEP, prompt diagnosis and treatment of cases, and ensuring high vaccination coverage within households and communities are key to preventing secondary transmission
Education on recognizing early symptoms and seeking medical care is crucial.
Monitoring Of Symptomatic Contacts:
Symptomatic contacts should be monitored closely for signs of respiratory distress, apnea, or other severe manifestations
Hospitalization may be required for infants, those with severe symptoms, or those at high risk for complications.
Key Points
Exam Focus:
Remember the timing for PEP: initiate within 3 weeks of last exposure
Macrolides are the drug of choice for PEP
Azithromycin is favored for its dosing regimen and tolerability
Tdap vaccination in pregnant women is crucial for neonatal protection.
Clinical Pearls:
Always inquire about the vaccination status of all household members
Consider early Tdap vaccination for infants exposed to pertussis
Differentiate between the catarrhal and paroxysmal stages to guide management and suspect pertussis.
Common Mistakes:
Not offering PEP to all household contacts, especially asymptomatic adults
Delaying PEP initiation
Forgetting Tdap vaccination in pregnant women or unvaccinated adults in contact with infants
Misdiagnosing pertussis in adolescents and adults due to atypical presentation.