• Clinical science

Pertussis (Whooping cough…)

Abstract

Pertussis, or whooping cough, is a highly infectious disease of the respiratory tract caused by the gram-negative bacteria Bordetella pertussis. The disease is mainly transmitted via airborne droplets and is most commonly occurs in children. Typically, pertussis manifests in three stages, with the second and third stage characterized by an intense paroxysmal coughing that is followed by a distinctive whooping sound on inhalation and, in some cases, vomiting. Young infants may not develop the typical cough, and often present with apnea and cyanosis instead. The disease is most often diagnosed via laboratory tests, especially detection of B. pertussis in bacterial culture. However, as test results may take time to obtain, treatment should be initiated as soon as clinical suspicion of pertussis arises. Subsequent management includes hospitalization of high-risk patients (e.g., infants) and antibiotic therapy with macrolides. These may lessen the length and severity of the disease if administered early, while also reducing infectivity and further disease transmission. Macrolides are also the drug of choice for post-exposure prophylaxis (PEP), which is recommended for all people with a recent history of exposure to pertussis. PEP is administered regardless of the individual immunization status, as both vaccination and prior infection may shorten the disease course, but do not provide full immunity.

Epidemiology

  • Typically a childhood disease (particularly children aged < 1 year); however, older patients are increasingly affected
  • High rate of infections in newborns: no transfer of maternal immunity (passive immunity) The exact etiology is unknown. A possible explanation is that no long-lasting immunity against pertussis can be established. Therefore, many mothers may not have sufficient antibodies to provide passive immunity.

References:[1][2][3][4]

Epidemiological data refers to the US, unless otherwise specified.

Etiology

  • Pathogen: Bordetella pertussis is a gram‑negative, obligate aerobic coccobacillus
  • Transmission: airborne droplet (through coughing); direct contact with oral or nasal secretions
  • Infectivity
    • Without antibiotic treatment: 4–6 weeks
    • With treatment: ∼ 5 days
    • The end of the incubation period marks a rise in infectivity; it is particularly high during catarrhal stage, but gradually recedes in paroxysmal stage (see “Stages” below).
    • Highly virulent
  • Incubation period: on average 7–10 days (range 4–21 days)

References:[2][4]

Pathophysiology

References:[4][5][6][7]

Stages

Catarrhal stage (∼ 1–2 weeks)

  • Nonspecific symptoms similar to an upper respiratory infection (mild cough, watery nasal discharge, rarely low-grade fever)
  • Possibly conjunctivitis

Paroxysmal stage (∼ 2–6 weeks)

  • Intense paroxysmal coughing (often occurring at night)
    • Followed by a deep and loud inhalation or high-pitched “whooping” sound
    • Accompanied by tongue protrusion , gagging, and struggling for breath
    • Possibly accompanied by cyanosis
    • Increases in frequency and severity throughout the stage
  • Followed by the expulsion of phlegm or posttussive vomiting (risk of dehydration)
  • Potential bleeding of the conjunctiva, petechiae, and venous congestion
  • In infants (< 6 months): risk of apnea; infants may not develop the typical cough and only manifest with apnea → close monitoring necessary!

Convalescent stage (weeks to months)

  • Progressive reduction of symptoms
  • Coughing attacks may persist over several weeks before resolving

The typical whooping cough manifests mainly in children aged 6 months to 5 years. The disease stages may be indistinguishable in young infants and adults!

References:[4][8][9]

Diagnostics

A presumptive diagnosis of pertussis may be made based on clinical history and findings. However, if possible, laboratory tests should be performed to confirm the diagnosis.

History

  • Clinical diagnosis possible in patients with a cough lasting ≥ 2 weeks and at least one of the following symptoms:
  • Inquire about immunization history and possible contact with infectious persons.

Laboratory tests

  • Blood count: lymphocyte-predominant leukocytosis (50,000–60,000/μL) that corresponds with disease severity
  • Pathogen detection (to confirm the diagnosis)
    • Culture (gold standard) or PCR: samples from deep nasopharyngeal aspiration or posterior nasopharyngeal swab
    • Serology: unsuitable for early diagnosis because antibody detection (IgA, IgG, IgM) first occurs after a period of 2–4 weeks

As B. pertussis only grows on respiratory epithelium, blood cultures are always negative!

References:[4][9][10][11]

Differential diagnoses

References:[4]

The differential diagnoses listed here are not exhaustive.

Treatment

General approach

  • Early initiation of treatment, especially in high-risk patients (e.g., infants), while confirmatory laboratory tests are pending
  • Hospitalization and monitoring: infants < 4 months; severe cases (e.g., respiratory distress, cyanosis, apnea, inability to feed)
  • Oxygen administration with humidification
  • Increased fluid intake and nutritional support
  • If necessary, sedation

Medical therapy

References:[4][12][13][14]

Complications

References:[4][15][16]

We list the most important complications. The selection is not exhaustive.

Prognosis

  • In children > 3 months: very good; lengthy convalescence, but full recovery
  • In children < 3 months: mortality 1–3%, particularly due to apnea
  • Increased risk for complications: premature infants; children < 6 months; people with underlying cardiac, pulmonary, neurologic, or neuromuscular disease

References:[4][12]

Prevention

  • Immunization
    • Children
      • Routine immunization: administer DTaP vaccine (diphtheria, tetanus, and pertussis) at 2, 4, 6, and 15–18 months, as well as 4–6 years (see immunization schedule)
      • Booster vaccination: administer Tdap vaccine:
        • Single dose at 7–10 years of age if immunization is incomplete;
        • Single-dose boost at 11–18 years of age, at least 10 years following the last dose
      • Contraindications: known anaphylactic reactions, encephalopathy following previous vaccination
    • Adults
      • One-time dose of Tdap
      • In particular, pregnant women and people in contact with newborns should be vaccinated! → increases passive immunity
  • Post-exposure prophylaxis: choice of antibiotics identical to treatment recommendations (see “Therapy” above)
    • Household and close contacts of infected people; especially people at risk of developing complications or close contacts of high-risk individuals (see “Complications” above)
    • Administered regardless of immunization status
  • Isolation: for 5 days after initiation of antibiotic therapy
    • Without antibiotic treatment: minimum of 3 weeks after the onset of first symptoms
  • Reporting: Pertussis is a notifiable disease

References:[17][2][4][12][14][18][19][20][21][22][23][24]