12 March 2012
- Pertussis (whooping cough) is an important cause of infant death worldwide and continues to be a public health concern even in countries with high vaccination coverage.
- Estimates from WHO suggest that, in 2008, about 16 million cases of pertussis occurred worldwide, 95% of which were in developing countries, and that about 195 000 children died from the disease.
- Pertussis is caused by the bacterium Bordetella pertussis which is transmitted from infected to susceptible individuals through droplets.
- Pertussis vaccine (combined with diphtheria toxoid and tetanus toxoid) has been part of WHO’s Expanded Programme on Immunization since its inception in 1974, and in 2008 about 82% of all infants worldwide received 3 doses of pertussis vaccine. WHO estimates that in 2008 global vaccination against pertussis averted about 687 000 deaths.
- Following an incubation period of 9–10 days (range, 6–20 days), patients develop catarrhal symptoms, including cough. During the course of 1–2 weeks, coughing paroxysms ending in the characteristic whoop may occur. In typical cases, cough is particularly severe at night and frequently followed by vomiting.
- In young infants, pertussis may cause apnoea and cyanosis without cough, whereas in adolescents and adults, uncharacteristic, persistent cough may be the only manifestation. The catarrhal, paroxysmal and convalescent stages of the disease may last for several months.
- Although most cases of clinically recognizable pertussis occur in children aged 1–5 years, severe disease and death have been reported mainly during the first weeks and months of life.
- Traditionally, bacterial culture has been considered the gold standard for laboratory confirmation. Bacterial culture is specific but not very sensitive, and requires selective culture media.
- Polymerase chain reaction (PCR) for Bordetella is more sensitive and can be performed on the same biological samples used for cultures.
- Serological diagnosis is based on detecting a significant increase in the concentration of specific antibodies against Pertussis Toxin (PT) in paired serum samples.
- The samples should be collected during the early catarrhal stage (acute serum) and about 1 month later (convalescent serum)
- For several decades, infant immunization programmes using pertussis vaccines of documented quality have been highly successful in preventing severe pertussis in infants all over the world.
- Two types of pertussis vaccines are available: whole-cell (wP) vaccines based on killed B. pertussis organisms, and acellular (aP) vaccines based on highly purified, selected components of this agent.
- A randomized controlled trial of 3-component and 5-component aP-containing vaccines compared with a wP vaccine concluded that the efficacies of the wP vaccine and the aP vaccines were similar against culture confirmed pertussis
- WHO recommends a 3-dose primary series, with the first dose administered at age 6 weeks; subsequent doses should be given 4–8 weeks apart, at age 10–14 weeks and 14–18 weeks. The last dose of the recommended primary series should be completed by the age of 6 months.
- All infants, including those who are HIV-positive, should be immunized against pertussis.
- At least 90% coverage of infants with 3 doses of high quality pertussis vaccines remains the programme priority worldwide, particularly where pertussis still poses a serious health problem in infants and young children.
- Although vaccination can prevent pertussis in adolescents and adults, there is insufficient evidence to support the addition of vaccine boosters in these age groups for achieving the primary goal of reducing severe pertussis in infants.
- Countries with demonstrable nosocomial transmission are encouraged to vaccinate health-care workers, particularly maternity and paediatric staff, if economically and logistically feasible.