Infectious Disease and Microbiology – Bordetella Species

Overview

Bordetella pertussis and Bordetella parapertussis are aerobic Gram-negative bacilli that cause respiratory tract infection, most notably whooping cough (pertussis). The organisms occur worldwide and can infect individuals who have previously been immunized, particularly adults, because protection against pertussis decreases over time.

Microbiology

Bordetella species are small, aerobic Gram-negative bacilli with a particular tropism for the respiratory tract. B. pertussis is the major cause of classic whooping cough, whereas B. parapertussis can produce a similar, often somewhat milder, pertussis-like respiratory illness.

Epidemiology

Pertussis has a worldwide distribution. Infection can occur even in previously vaccinated individuals because vaccine-induced immunity is not lifelong. Consequently, adolescents and adults may develop infection and can serve as sources of transmission to susceptible individuals, especially young infants.

Clinical Infection

The characteristic disease is whooping cough, a highly contagious respiratory infection. Illness typically begins with nonspecific upper respiratory symptoms and subsequently progresses to episodes of severe, repetitive coughing.

The classic paroxysmal stage is characterized by repeated coughing fits that may be followed by the characteristic inspiratory “whoop.” Post-tussive vomiting can occur. Infants may not develop the classic whoop and can instead present with apnea, cyanosis, or respiratory distress.

Diagnosis

Diagnosis can be established using a nasopharyngeal specimen. PCR provides rapid detection of Bordetella DNA and is commonly useful for confirming infection.

Culture may also be performed using specialized media, classically Bordet–Gengou medium. Culture is highly specific but becomes less sensitive as the illness progresses or after antibiotic therapy has begun.

Serologic testing may provide additional diagnostic information in selected patients, particularly later in the course of illness. Antigen detection from nasopharyngeal secretions has also been described, although molecular testing is generally more useful.

Treatment

Macrolide antibiotics are the principal antimicrobial therapy for pertussis. Treatment is most effective when started early and is particularly important for reducing transmission.

Traditional regimens include erythromycin, while azithromycin and clarithromycin are commonly used alternatives because they allow shorter treatment courses and are generally better tolerated.

The source regimen lists:

Erythromycin: 2 g/day orally in four divided doses for 14 days.

Azithromycin: 500 mg orally on day 1, followed by 250 mg once daily on days 2–5.

Clarithromycin: 500 mg orally every 12 hours for 7 days.

Antibiotics given after the paroxysmal cough has become established may have limited ability to shorten the cough itself, although treatment remains valuable for decreasing bacterial transmission.

Alternative Treatment

Trimethoprim–sulfamethoxazole (TMP-SMX) may be used when macrolides cannot be given. The listed adult regimen is one double-strength tablet orally every 12 hours for 7 days.

Antibiotic selection and dosing should be adjusted for age, pregnancy, contraindications, and current treatment guidelines.

Symptomatic Management

The cough associated with pertussis can persist for weeks despite appropriate antimicrobial treatment. Conventional cough suppressants, including codeine, are generally ineffective and are not routinely useful for controlling the characteristic paroxysmal cough.

Supportive management is particularly important in infants and patients with severe disease, who may require monitoring for apnea, hypoxemia, dehydration, or feeding difficulties.

Prevention and Infection Control

Pertussis is highly transmissible through respiratory droplets. Appropriate respiratory/droplet isolation precautions are therefore important during the infectious period.

Vaccination remains the major preventive strategy. Because immunity decreases with time, booster immunization is important for maintaining population protection and reducing transmission to vulnerable infants.

High-Yield Clinical Pattern

A patient with an initial mild upper respiratory illness followed by recurrent paroxysms of severe cough, inspiratory whooping, and post-tussive vomiting should raise strong suspicion for pertussis.

The diagnosis is supported by nasopharyngeal PCR or culture, and treatment is generally with a macrolide antibiotic.

Exam Essentials

Organisms: Bordetella pertussis and Bordetella parapertussis

Microbiology: Aerobic Gram-negative bacilli

Distribution: Worldwide

Major disease: Whooping cough (pertussis)

Transmission: Respiratory droplets

Classic symptom: Paroxysmal cough with inspiratory whoop

Diagnosis: PCR or specialized culture; serology may assist in selected cases

Classic culture medium: Bordet–Gengou medium

Treatment: Macrolides, especially azithromycin, clarithromycin, or erythromycin

Alternative: TMP-SMX

Cough suppressants: Usually ineffective

Prevention: Vaccination and appropriate respiratory/droplet precautions

Important pearl: Previous vaccination does not completely exclude pertussis, particularly in adolescents and adults whose immunity has waned.