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 cyclical increase occurred in 2016, but cases have been rising across England and many other countries since December 2023.
Whooping cough was endemic in the UK before the introduction of 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.
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 2016 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 local health protection team will recommend appropriate tests based on the individual’s age, duration of symptoms, and available laboratory facilities. The available tests include:
Culture and Isolation:
- Suitable for individuals of all ages with a cough lasting less than 21 days.
- This involves using nasopharyngeal aspirate (NPA) or nasopharyngeal swab (NPS)/pernasal swab (PNS).
- The NHS laboratories conduct these tests, and confirmed isolates are sent to the Respiratory and Vaccine Preventable Bacteria Reference Unit (RVPBRU).
PCR (Polymerase Chain Reaction):
- This molecular technique detects DNA sequences of Bordatella pertussis
- It is also suitable for individuals of all ages with a cough lasting less than 21 days.
- PCR is generally more sensitive than culture as it does not require viable organisms; however, it is less likely to be positive in individuals with symptoms for 21 days or more.
- PCR testing is available from regional UK Health Security Agency (UKHSA) laboratories, with positive samples sent to RVPBRU.
Serology:
- Suitable for older children (over 16 years) and adults who have had a cough for more than 14 days and at least one year after their most recent whooping cough vaccine dose (including doses administered during pregnancy).
- Serology detects antibodies to the whooping cough toxin and is useful for cough durations of 21 days or more when culture and PCR are unlikely to be positive.
- Serology is available from RVPBRU.
Oral Fluid Testing (OFT):
- Suitable for children aged 2–16 years with a cough history of more than 14 days and at least one year after the most recent whooping cough vaccine dose.
- OFT tests for anti-pertussis toxin immunoglobulin G (IgG).
- The health protection team sends OF kits to patients upon notification, and samples are tested and reported by RVPBRU.
Whooping cough is confirmed by the presence of clinical features plus one of the following:
- Isolation of Bordatella pertussis from a respiratory sample, typically NPA or NPS/PNS (or throat swab).
- A positive Bordatella pertussis PCR result in a respiratory clinical specimen.
- An IgG titre greater than 70 International Units per millilitre (IU/ml) from a serum specimen, or greater than 70 arbitrary units (aU) from an oral fluid specimen, in the absence of vaccination within the past year.
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.
The UK Health Security Agency recommends that children with whooping cough be kept away from school, nursery or childminders for 48 hours from starting appropriate 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 UK Health Security 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.
