Whooping cough is a highly contagious respiratory disease caused by the Bordetella pertussis bacterium. It is an airborne infection, spread by direct contact between infected people. In regions without a child vaccination program, transmission occurs from one child to another. However, in regions where child vaccination programs have been in place for decades, transmission is now occurring between adults and infants. Whooping cough does not convey lifelong immunity, and a person may become infected more than once in his or her life.
Symptoms and diagnosis confirmation
Typical clinical whooping cough is characterized by three phases. The first is a symptomless incubation period, followed by atypical rhinorrhea lasting about two weeks. The second phase is the paroxysmal stage, lasting over a week and characterized by a persistent cough, in most cases without any fever. Bouts of coughing are combined with difficulty inhaling, apnea or cyanosis. Vomiting may occur after the coughing fits. Symptoms are usually worse at night in teenagers and adults. Lastly, the disease enters the convalescent stage, which may last from one to several weeks. In young children, major complications include types of pneumonia or neurological disorders (seizures, encephalitis).
Whooping cough can be extremely serious, even fatal, in infants. Clinical characteristics can vary - particularly in adults, who may have residual immunity. This is why laboratory diagnosis is vital, to prevent transmission of this highly contagious disease and protect people who are in contact with the infected person.
The incidence of this disease has greatly reduced in countries where there is widespread vaccination of young children. However, there are still between 40 and 60 million cases of whooping cough reported in the world each year, causing around 300,000 deaths, most of them occurring in developing countries. These figures nevertheless represent a gross underestimation, since not all countries have a surveillance system in place.
Changes in transmission mode
Countries that have had a widespread vaccination program in place for over fifty years, such as Australia, Belgium, Canada, the USA, Finland, France, the Netherlands and the United Kingdom, have seen a change in the transmission mode of the disease. The policy not to administer booster vaccinations after the age of eighteen months has led to transmission occurring not between children, as it did before the advent of vaccination campaigns, but from teenagers and adults to newborns. In the past, the recommendation was against the administration of booster vaccinations, based on a possible increase in side effects caused by the repeated use of whole-cell vaccines.
The situation in France
Surveys carried out in 1991, 1993-94, 1999-2000, 2005 and 2009-10 by the Institut Pasteur, and surveillance undertaken since 1996 by the RENACOQ national whooping cough surveillance network (comprising 42 hospital pediatricians and the same number of hospital bacteriologists, as well as the Institut Pasteur and the French Institute for Public Health Surveillance), show that this trend is also reflected in France. This is why a late booster vaccination has been recommended since 1998 for adolescents (given between the ages of 11 and 13). Furthermore, in 2004 the cocooning strategy was introduced (i.e. vaccination for all adults in contact with a newborn infant, parents, grandparents, childminders and nannies, etc.), at-risk adults and health workers in contact with newborns. Such booster vaccines were made possible by the development of subunit or acellular vaccines (made from inactivated bacterial proteins) specially adapted for newborns, teenagers or adults. Other countries, such as Germany, Austria, Australia, Canada and the USA, rapidly followed suit. However, with vaccination coverage remaining very low in adults, whooping cough vaccination has been recommended in France since 2008 for all adults vaccinated over ten years previously, along with health professionals and staff working in institutions - particularly those caring for newborns or the elderly. Since april 2013, new recommendations were introduced (see below).
The only laboratory tests reimbursed under the French health scheme are isolation of the bacterium or detection of its genetic material by PCR, from nasopharyngeal aspirates or swabs.The PCR diagnosis is a very sensitive one but is a Bordetella diagnosis, not specific of B. pertussis.
Macrolides are the preferred antibiotics, eliminating the bacterium from secretions, thus reducing the risk of contamination. Antibiotic therapy is recommended for all people in close contact with a patient, irrespective of their age and if their booster vaccination is older than five years.
In France, vaccination is recommended for children from the age of two months or eight weeks. The vaccination schedule consists of two injections at 2 and 4 months. The whooping cough vaccines are combined with vaccines against tetanus, diphtheria, poliomyelitis, Haemophilus b and sometimes hepatitis B. Boosters are given at 11 months, 6 years, 11-13 years and 25 years, the cocooning strategy being maintained. Vaccines for adolescents and adults are combined vaccine that also protects against tetanus, diphtheria and poliomyelitis.
At the Institut Pasteur
The Molecular Prevention and Therapy of Human Diseases Unit, led by Nicole Guiso, houses the National Reference Center for Pertussis and other Bordetella, which is responsible for, amongst other things, monitoring changes in the number of circulating Bordetella pertussis isolates and other species of Bordetella. This center is part of the national whooping cough surveillance network, in association with the French Institute for Public Health Surveillance, the RENACOQ network and primary care pediatricians in the ACTIV network. In addition to analyzing clinical isolates, it develops new biological diagnostic tests, which it then transfers to bacteriologists in the RENACOQ network.
The research unit is also part of a European network known as "Eupertstrain", responsible for carrying out detailed analysis of the isolates circulating in Europe. The unit analyzes the impact of vaccination on the immunity of the population and the target pathogen. It also aims to develop therapeutic tools and improve prevention.
Surveillance and public health : National Reference Center for Pertussis and other Bordetella led by Nicole Guiso