Paediatrician, Specialist in Neonatology
HPA Magazine 7
Over the past 30 years, in various countries, there has been an increase in the incidence of whooping cough, especially in adolescents and adults, in spite of widespread vaccination. Whooping cough is an infectious disease of the respiratory tract caused by the bacterium Bordetella pertussis.
The classic clinical profile is characterised by 3 stages: the first resembles a common cold, with a dry cough and low fever; the second (which can last 2 – 6 weeks) includes a worsening of the cough, facial congestion, protrusion of the tongue and often “whooping” or vomiting; the third is the progressive lessening of the cough, but sometimes lasting for months. Because of this drawn-out duration, which can last as long as 12 weeks, it is also known as the “100-day cough”.
The eradication of avoidable infectious diseases continues to be a priority. Before vaccination of children was introduced in 1940, whooping cough was one of the main causes of death among children.
In Portugal, vaccination against whooping cough was introduced in the National Vaccination Program (PNV) in 1965. From 1967, it became possible to observe the high impact of vaccination against this disease in the marked decrease in the number of cases reported.
The universal vaccination of children resulted in a significant reduction in morbidity and mortality. Starting from the decade of the 90s, there has been an increase in reports of cases of whooping cough in several countries. It has not only become the most prevalent of the preventable diseases in the industrialised countries, it is also the only disease with a specific vaccine that has increased in the last few years. This apparent resurgence of the disease is therefore worrying for the public health sector.
The principal explanation put forth for such an increase in the incidence is the loss of immunity, which happens after natural infection and vaccination. The epidemiological impact of this fact depends essentially on the durability of protection within the population, which continues to be notoriously difficult to estimate. Furthermore, the immunity given by the vaccine begins to decrease within 3 to 6 years following the complete immunisation and/or the second reinforcement (at 6 or 7 years of age), becoming negligible after 12 years of age, the reason that also explains why whooping cough is currently endemic among adolescents and young adults.
The resurgence of whooping cough is also attributed to various other factors, among which is the greatest clinical suspicion of the disease: the adoption of less efficient vaccines and the adaptation of the bacteria.
Although whooping cough only results in a prolonged cough for older children and adults who, in many cases, only manifest a slight discomfort, its presence in the community inevitably gives rise to infections in non-immunised infants, who are subject to the risks of serious complications and death.
Whooping cough is a highly contagious endemic bacterial infection, with epidemic spikes that tend to occur every 3 to 5 years. Bordetella pertussis only infects humans. In children, the source of infection by these bacteria is almost always attributed to members of the family, often the parents or older siblings. In areas of high levels of vaccination, adolescents and adults are the main source of bacteria. However, in places where vaccination levels are low, children are the main source of transmission of the disease.
Contagion occurs by contact with respiratory droplets resulting from coughing or sneezing by infected people, especially in the catarrhal stage and the beginning of the paroxysmal stage (when the bursts, or numerous rapid coughing starts). This facilitates transmission because generally the diagnosis is only suspected later, when the cough has already lasted more than 21 days.
Whooping cough can occur at any age, but the majority of the cases are notified and, probably, recognised in children under 5 years of age. There is insufficient maternal protection by trans-placental transmission of antibodies and babies are susceptible from the first weeks of life.
Universal vaccination of adolescents and adults, as well as maternal vaccination during gestation1, or immediately following childbirth, and in adults who will have intimate contact with the newborn are potential means of individual protection and interruption of transmission to susceptible infants, with the consequent reduction of morbidity and mortality.
If you have any family member, including babies and children with chronic and/or prolonged cough, please consult your doctor.