Cause
Whooping cough is a highly contagious respiratory infection mainly caused by the bacterium Bordetella pertussis.
The disease may also be caused by Bordetella parapertussis. The incidence of infections due to this second agent is highly variable from one country to another and is low in France.
Whooping cough is an airborne infection, spread by direct contact with infected people. In regions without a child vaccination program, transmission occurs among children. However, in regions like France where child vaccination programs have been in place for decades, whooping cough is now being transmitted essentially from adults or adolescents to infants. Since neither whooping cough nor the vaccine confer lifelong immunity, it is possible to contract the disease more than once.
Symptoms and diagnosis confirmation
Typical whooping cough is characterized by three phases:
(1) an incubation period which is initially asymptomatic, followed by rhinorrhea (runny nose) lasting approximately two weeks;
(2) a paroxysmal stage characterized by a persistent cough lasting over a week, in most cases without any fever. Bouts of coughing are combined with difficulty inhaling, and vomiting may occur after coughing fits. Infants may experience apnea, sometimes combined with bradycardia, or cyanosis during coughing fits. In adolescents and adults, the symptoms are generally worse at night;
(3) the third stage of whooping cough is the convalescent stage, which may last for several weeks. In young children, the main complications include pneumonia and neurological disorders (seizures or encephalitis). In infants, whooping cough can be extremely serious or even fatal, causing respiratory failure or multiple organ failure.
Clinical characteristics may vary, especially in adolescents or adults depending on their immune status. Laboratory diagnosis of whooping cough is therefore vital so that the patient may be treated with antibiotics as quickly as possible, thus rapidly preventing transmission of this highly contagious disease and protecting people who are in contact with the infected individual.
Epidemiology
The incidence of whooping cough has fallen considerably in countries that have introduced routine vaccination programs for young children. But in 2014, the World Health Organization (WHO) estimated that there were still 24 million cases of whooping cough worldwide in children under the age of 5, and around 160,700 deaths each year. Most cases are reported in developing countries. The real figures are undoubtedly much higher, since not all countries have introduced a surveillance system.
New modes of transmission
Whooping cough vaccination with an inactivated whole-cell vaccine was introduced in the 1940s and 1950s. Countries that implemented vaccination, including France, most of Europe, Australia, Canada and the United States, saw a change in the way the disease was transmitted. Unlike in the pre-vaccine era, whooping cough was no longer passed from child to child; it now tended to be transmitted from adolescents and adults to unvaccinated or partially vaccinated infants as a booster was not yet offered. This was not recommended at the time due to side effects suspected to be caused by repeated vaccinations with the inactivated whole-cell vaccine.
The situation in France : surveillance and vaccinations
Following research carried out in hospitals confirming circulation of the bacteria in infants, and given that surveillance of whooping cough through compulsory notification had been discontinued a decade earlier, a surveillance network of the pediatric forms observed in hospitals (the national whooping cough network or RENACOQ) was set up in 1996. This network coordinated by Santé publique France is composed of pediatricians and bacteriologists, based in hospitals, who work with the National Reference Center for Whooping Cough (hosted at the Institut Pasteur) and Santé publique France.
Boosters were made possible by the development and availability of acellular vaccines (composed of purified and inactivated bacterial proteins) that are suitable for infants, adolescents and adults:
- Since 1998, health authorities have recommended a late booster vaccination between the ages of 11 and 13;
- Since 2004 a booster has also been recommended for people in close contact with newborn infants (parents, grandparents, childminders and nannies, etc. and also healthcare professionals). This vaccination strategy, known as cocooning, is aimed at creating a barrier around infants during their first 6 months. But given the persistently low vaccine coverage in adults, in 2008 France recommended booster vaccination for all adults and in particular for all healthcare professionals and people working in community care, especially those in contact with infants or the elderly.
- In 2013, the whooping cough vaccination schedule was simplified to two injections at 2 months (8 weeks) and 4 months followed by a booster at 11 months. These injections include an acellular pertussis vaccine combined with the tetanus, diphtheria, polio, Haemophilus b and hepatitis B vaccines. Boosters are recommended at age 6, then age 11-13 and in young adults at the same time as the 10-yearly tetanus-diphtheria-polio booster (at age 25), if they have not had a whooping cough vaccine in the past 5 years. Adults over the age of 25 who have not had this booster may have a catch-up vaccine up to the age of 39. As part of the cocooning strategy, a booster is recommended for all adults in contact with infants (parents, grandparents, childminders and nannies, etc.). Finally, a booster vaccination is recommended for healthcare workers and people working in the community, especially those in contact with infants and the elderly, every 20 years from age 25.
- Since January 1, 2018, whooping cough vaccination has been compulsory in France for children from the age of two months.
Diagnosis
The only laboratory tests that are reimbursed under the French social security system are isolation of the bacterium (in culture) or detection of genetic material by PCR, from nasopharyngeal aspirates or swabs. Serology is not recommended as it is considered unreliable and has not been reimbursed since 2011.
Treatment of cases and contacts
Antibiotic therapy, most often with macrolides, eliminates the bacteria from secretions, thereby reducing the risk of transmission. Antibiotic therapy is recommended for anyone in close contact with the patient, even if they are not yet experiencing any symptoms and irrespective of their age, if they have not had a booster vaccination in the past five years.
At the Institut Pasteur
The Biodiversity and Epidemiology of Bacterial Pathogens Unit, led by Sylvain Brisse, hosts the National Reference Center (CNR) for Whooping Cough and other Bordetella Infections, which is in charge of monitoring the development of circulating strains, alerting the health authorities in the event of an unusually severe outbreak and providing guidance to doctors and medical test laboratories.
The research unit is also part of a European surveillance network responsible for analyzing isolates circulating in Europe. Current research projects are focusing on the impact of vaccination on population immunity and on Bordetella pertussis strains.
July 2021
The Institut Pasteur teams working on whooping cough
Research units
Biodiversity and Epidemiology of Bacterial Pathogens Unit led by Sylvain Brisse
BiophysiCyaA Group: Biophysical investigation of the Bordetella pertussis adenyl cyclase (CyaA) toxin led by Alexandre Chenal
Surveillance and public health
National Reference Center for Pertussis and other Bordetella led by Nicole Guiso
