Is Whooping Cough Contagious?

Introduction

Whooping cough, also known as pertussis, is a highly contagious respiratory disease caused by the bacterium Bordetella pertussis. It primarily affects infants and young children, although adults and adolescents can also contract the disease, especially if their immunity from vaccination or previous infection has waned  .

The Contagious Nature of Whooping Cough

Whooping cough spreads through respiratory droplets when an infected person coughs or sneezes. The disease is characterized by severe coughing spells that can last for weeks and are often followed by a high-pitched “whoop” sound during the subsequent inhalation. The incubation period of pertussis is typically 7 to 10 days, but it can range from 5 to 21 days .

The contagious period for pertussis starts from the onset of the catarrhal stage, which resembles a common cold, and continues until about three weeks after the onset of coughing fits. Antibiotic treatment can shorten this period of contagion. Infants and unvaccinated individuals are at the highest risk of contracting and spreading the disease  .

Molecular Structure of Pertussis Toxin: This depicts the pertussis toxin composed of five subunits: S1 (green), S2 (cyan), S3 (purple), S4 (yellow, double), and S5 (red).

Clinical Features and Complications

Pertussis manifests in three stages: the catarrhal stage, the paroxysmal stage, and the convalescent stage. During the catarrhal stage, symptoms are mild and similar to a common cold, including runny nose, mild cough, and fever. This stage lasts one to two weeks and is when the disease is most contagious.

The paroxysmal stage follows, characterized by severe coughing fits that can result in vomiting and exhaustion. This stage can last from one to six weeks or longer. The final convalescent stage is marked by a gradual recovery, but coughing spells may continue for weeks or even months.

Complications from pertussis are more common in infants and can include pneumonia, convulsions, encephalopathy, and failure to thrive due to vomiting. In severe cases, pertussis can be fatal, particularly in infants younger than six months.

Diagnosis

Diagnosing pertussis involves a combination of clinical evaluation and laboratory tests. Common diagnostic methods include:

1. Polymerase Chain Reaction (PCR): PCR is a highly sensitive test that detects Bordetella pertussis DNA in nasopharyngeal swabs. It is most effective during the early stages of the disease.
2. Culture: Although considered the gold standard, culture has lower sensitivity, particularly in the later stages of the disease or after antibiotic treatment has started.
3. Serology: Serological tests measure antibodies against pertussis toxin. They are useful for diagnosing pertussis in later stages, especially in older children and adults  .

Treatment

Antibiotic Treatment

1. Macrolides: The first-line treatment for pertussis includes macrolide antibiotics such as azithromycin, clarithromycin, and erythromycin. These antibiotics are effective in reducing the duration of infectiousness and, if administered early, can also reduce the severity and duration of symptoms.
2. Azithromycin: Often preferred due to its shorter course (typically five days) and better tolerance compared to erythromycin.
3. Clarithromycin: Similar in effectiveness to azithromycin but requires a seven-day course.
4. Erythromycin: Traditionally used but associated with gastrointestinal side effects and requires a 14-day course.
5. Alternative Antibiotics: For patients who cannot tolerate macrolides, trimethoprim-sulfamethoxazole can be used as an alternative.

Supportive Care

1. Hydration and Nutrition: Ensuring adequate hydration and nutrition is crucial, especially for infants who may suffer from vomiting after coughing fits.
2. Hospitalization: Severe cases, particularly in infants, may require hospitalization for supportive care such as oxygen therapy and intravenous fluids.

Preventive Measures

1. Vaccination: The primary prevention strategy for pertussis is vaccination. The DTaP vaccine (diphtheria, tetanus, and acellular pertussis) is administered in a series of shots at 2, 4, 6, and 15-18 months of age, with a booster at 4-6 years. The Tdap booster is recommended for adolescents, pregnant women, and adults to maintain immunity.
2. Post-exposure Prophylaxis: Close contacts of a pertussis case, particularly those at high risk, such as infants and pregnant women, should receive antibiotics to prevent the spread of the disease.

Global Impact and Surveillance

Despite widespread vaccination efforts, pertussis remains a significant public health concern worldwide. The resurgence of pertussis in some high-vaccination countries has been attributed to several factors, including waning immunity, changes in the bacterium, and improved diagnostic methods.

According to a review in The Lancet, pertussis causes nearly 300,000 deaths annually, predominantly in unvaccinated children in developing countries. Efforts to improve vaccination coverage and timeliness, along with better surveillance, are crucial in controlling the spread of pertussis globally.

Conclusion

Whooping cough is highly contagious and can lead to severe complications, especially in infants and young children. Early diagnosis, appropriate antibiotic treatment, and vaccination are key strategies in managing and preventing pertussis. Public health efforts must continue to focus on increasing vaccination coverage and improving disease surveillance to mitigate the impact of this potentially deadly disease.

References

1. Crowcroft, Natasha S., and Richard G. Pebody. “Recent developments in pertussis.” The Lancet 367.9526 (2006): 1926-1936.

2. Nieves, Delma J., and Ulrich Heininger. “Bordetella pertussis.” Emerging Infections 10 (2016): 311-339.

3. Kilgore, Paul E., et al. “Pertussis: microbiology, disease, treatment, and prevention.” Clinical microbiology reviews 29.3 (2016): 449-486.