Whooping cough (or pertussis) is a highly contagious respiratory infection caused by the bacterium Bordetella pertussis (and more rarely by B. parapertussis). It 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 from adults to infants. Since whooping cough does not confer lifelong immunity, it is possible to contract the disease more than once.
Symptoms and diagnosis confirmation
Typical clinical whooping cough is characterized by three phases. The first is an incubation period, initially symptomless and then followed by a runny nose lasting for about two weeks. Then comes the 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. The third stage of whooping cough is the convalescent stage, which may last for several weeks. In young children, major complications include pneumonia or neurological disorders (seizures or encephalitis). In infants, whooping cough can be extremely serious or even fatal, causing respiratory failure or even multiple organ failure.
Clinical characteristics may vary, especially in adolescents or adults depending on their immune status. This is why laboratory diagnosis of whooping cough is vital, to prevent transmission of this highly contagious disease as quickly as possible and protect people who are in contact with the infected individual.
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
In countries where routine vaccination was introduced more than 50 years ago, such as France, Australia, Belgium, Canada, Finland, the Netherlands, the United Kingdom and the United States, we are currently witnessing a change in the way the disease is spread, mainly as a result of children not being given the booster after the age of 18 months. Unlike in the pre-vaccine era, whooping cough is no longer passed from child to child; it now tends to be transmitted from adolescents and adults to unvaccinated or partially vaccinated infants. Booster vaccinations were not previously recommended because of a potential increase in side effects caused by repeated vaccinations with inactivated whole-cell bacterial vaccines.
The situation in France
Following research carried out in hospitals from 1993 to 1994 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 is composed of 42 pediatricians and 42 bacteriologists, based in hospitals, who work with the National Reference Center for Whooping Cough (hosted at the Institut Pasteur) and Santé publique France.
Since 1998, health authorities have recommended a late booster vaccination between the ages of 11 and 13, and since 2004 this has also been recommended for people in close contact with newborn infants (parents, grandparents, childminders or nannies, etc. and also healthcare professionals). These boosters were made possible by the development and availability of acellular vaccines (composed of inactivated bacterial proteins) that are suitable for infants, adolescents and adults. Other countries including Australia, Austria, Canada, Germany and the United States have decided to introduce a vaccination strategy known as cocooning. But given the persistently low vaccine coverage in adults, in 2008 France introduced recommended vaccination for all adults (every 20 years from the age of 25) and in particular for all healthcare professionals and people working in community care, especially in neonatal units or retirement or nursing homes.
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 unreliable; it has not been reimbursed since 2011.
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.
Since January 1, 2018, whooping cough vaccination has been compulsory in France for children from the age of two months. The vaccination schedule consists of two injections at 2 months (8 weeks) and 4 months, followed by a booster at 11 months with the acellular pertussis vaccine combined with the tetanus, diphtheria, polio, Haemophilus b and hepatitis B vaccines.
Boosters are then 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.
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, raising the alarm in the event of an unusually severe outbreak and providing guidance to doctors and medical test laboratories. The aim of the CNR is also to develop new laboratory diagnosis methods and to evaluate new diagnostic kits brought to market.
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 investigating target pathogenic bacteria.
The Institut Pasteur teams working on whooping cough
Biodiversity and Epidemiology of Bacterial Pathogens Unit led by Sylvain Brisse
Surveillance and public health
National Reference Center for Pertussis and other Bordetella led by Nicole Guiso