Pertussis, also known as whooping cough, is an upper respiratory tract infection caused by the Gram-negative bacteria Bordatella pertussis. Transmission is via respiratory droplets and the incubation period is approximately 7-21 days. The disease is highly contagious and is transmitted to around 90% of close household contacts.
Epidemiology
Whooping cough is a cyclical disease with increases occurring every three to four years; the last peak occurred in 2012.
Whooping cough was endemic in the UK before introducing the vaccine in the 1950s, with annual notifications exceeding 120,000 in England and Wales.
Prevalence plummeted following the widespread uptake of the immunisation programme, but epidemics still occur periodically.
In the UK, whooping cough used to have its highest incidence in infants, but now infection also occurs in adolescents and adults. In the 2012 outbreak, the highest incidence of disease was in babies under the age of 3 months, who contracted the infection before being old enough to have their first vaccination. Whooping cough is underdiagnosed, with one study in primary care in the UK showing evidence of recent infection in one-fifth of school children presenting with a persistent cough.
Clinical features
The clinical course of whooping cough occurs in two stages:
- Catarrhal stage:
This phase presents similarly to any mild respiratory infection with low-grade pyrexia and coryzal symptoms. A cough can be present, but it is usually mild and nowhere near as pronounced as during the paroxysmal phase. The catarrhal phase usually lasts around a week.
- Paroxysmal stage:
The typical paroxysmal cough develops in this phase as the catarrhal symptoms start to settle. The coughing occurs in paroxysmal spasms, typically preceded by an inspiratory ‘whoop’ followed by a rapid succession of expiratory hacking coughs. There may be vomiting, and patients often develop subconjunctival haemorrhages and petechiae. Patients are generally well between spasms, and there are usually no chest signs present. This phase can be very protracted, lasting up to 3 months. There is usually a gradual recovery over this period, and the latter stages are sometimes referred to as the ‘convalescent stage’.
Documented complications of whooping cough include:
- Secondary pneumonia
- Rib fractures
- Herniae
- Syncopal episodes
- Encephalopathy
- Seizures
Diagnosis
The current recommendations of the Health Protection Agency (HPA) for testing for whooping cough depend upon both the age of the patient, length of time from onset of illness, and the severity of the presentation.
- Testing in infants under 12 months of age:
- Hospitalised patients should be investigated with PCR testing
- Non-hospitalised patients within 2 weeks of onset should be investigated with culture of nasopharyngeal swab or aspirate
- Non-hospitalised patients presenting over 2 weeks after onset should be investigated with serology for anti-pertussis toxin IgG antibody levels
- Testing in children over 12 months of age and adults:
- Patients presenting within 2 weeks of onset should be investigated with culture of nasopharyngeal swab or aspirate
- Patients aged 5 to 16 that have not received the vaccine within the last year, presenting over 2 weeks after onset, should have oral fluid testing for anti-pertussis toxin IgG antibody levels
- Patients aged under 5 or over 17 presenting over 2 weeks after onset should be investigated with serology for anti-pertussis toxin IgG antibody levels
Management
Hospital admission is required for any infant aged ≤6 months who is acutely unwell or at any age if there are respiratory difficulties or significant complications.
Although this is a bacterial disease, antibiotics do not alter the clinical course once the disease is established. Macrolide antibiotics, however, have been shown to shorten the period of infectivity. Antibiotics should therefore be given as soon as possible after the onset of illness in order to eradicate the organism and limit ongoing transmission.
Antibiotics should only be started within three weeks of the onset of symptoms, given their lack of effect on the course of the illness and the period of infectivity.
Macrolide antibiotics are used first-line:
- Clarithromycin for babies aged less than 1 month
- Azithromycin or clarithromycin for children aged 1 month or older and for non-pregnant adults
- Erythromycin for pregnant women.
Co-trimoxazole can be used off-licenced in circumstances where macrolides are contra-indicated or not tolerated.
Public Health England recommends that children with whooping cough be kept away from school, nursery or childminders for 5 days from starting antibiotic treatment, or 21 days from the onset of the illness if no antibiotic treatment. Parents and teachers should be warned that non-infectious coughing may persist for many weeks after treatment.
Chemoprophylaxis
The Health Protection Agency has identified two sets of priority groups for public health action in the contact management of whooping cough:
Group 1. At increased risk of severe or complicated infection (vulnerable)
- Infants under 1 year who have received less than 3 doses of pertussis vaccine
Group 2. At increased risk of transmitting infection to individuals in Group 1
- Pregnant women at greater than 32 weeks gestation
- Healthcare workers working with infants and pregnant women
- Individuals working with infants too young to be vaccinated (<4 months old)
- Individuals sharing a household with infants too young to be vaccinated (<4 months old)
Current guidance states that antibiotic prophylaxis with a macrolide antibiotic, such as erythromycin, should only be offered to close contacts when both of the following criteria have been met:
- Onset of disease in the index case is within the preceding 21 days, and;
- There is a close contact in one of the two priority groups
When these two criteria have been met, ALL contacts, regardless of vaccination status and age, should be offered chemoprophylaxis. Immunisation or a booster dose (depending on current vaccination status) should also be considered for those who have been offered chemoprophylaxis.
Header image used on licence from Shutterstock
Thank you to the joint editorial team of www.mrcgpexamprep.co.uk for this article.
