Whooping cough in adults

Case history

A 46-year-old female finance officer presents to morning surgery complaining of an unusual cough going on for 5 weeks. ‘I thought I had a bit of a cold, but now when I cough, it really hits hard’, she says. There is no relationship to the time of day and there are no exacerbating factors. She reports no fever, tiredness or coryzal symptoms and no haemoptysis, shortness of breath, weight loss, appetite loss or skin rashes. She is a non-smoker with no occupational risks and no history of tuberculosis. Indeed, she has no significant past medical history and is taking no medication. She reports that her husband has developed a similar cough. The patient appears well, and examination and observations are all normal.

A chest X-ray, blood tests (full blood count, renal function and inflammatory markers) and urine dip are all normal. Bordetella pertussis serology shows strongly positive for IgG B. pertussis antibodies. The patient is informed of the findings and advised that antibiotics will not be helpful and that the cough could last for 3 months, but should get better with time. The local Public Health England office are contacted to report the diagnosis and they set about contact tracing and offering antibiotics where appropriate to prevent further spread.

Discussion

Whooping cough is a bacterial infection caused by the bacterium B. pertussis and an often-overlooked cause of cough in adults. Diagnosis is commonly delayed or missed altogether. It typically starts as an upper respiratory tract infection (URTI), with a coryzal incubation period and coughing 7 to 10 days later. The diagnosis should be considered with any cough lasting more than 14 days, particularly if there are any distinguishing features: Inspiratory whooping, frightening attacks of choking and exhausting coughing, particularly interspersed between long intervals with no coughing. There is often post-tussive vomiting and an absence of fever. Obviously, exposure to a person with confirmed pertussis raises suspicion. It can present atypically without these features.

Although normally viewed as a childhood disease, in England, of the 2947 laboratory confirmed cases in 2018, more than 80% were in teenagers and adults. Childhood immunisation is no guarantee of protection as vaccine efficacy decreases with time. There may be a case for regular boosters.

Whooping cough is a notifiable disease as it is highly contagious. Suspected cases should be referred within 3 days to the local public health agency. Diagnostic testing should not delay use of antibiotics to prevent further spread, but only if started within 21 days of symptom onset. The local public health agency will advise on appropriate testing to confirm the diagnosis as it is not straightforward and depends on timing from symptom onset. Investigation may include polymerase chain reaction, bacterial culture, oral fluid kit and/or serology. They will also initiate infection control measures, such as contact tracing. If testing for B. pertussis is negative, but clinical suspicion remains, it may be caused by Bordetella parapertussis or other rarer types that probably account for up to 10% of Bordetella infections.

There are many other causes of chronic cough. Presentation and symptoms should guide the diagnosis. Other causes include gastro-oesophageal reflux disease, protracted viral URTIs, asthma or chronic obstructive pulmonary disease, post-infectious cough, atypical pneumoniae, post-nasal drip, upper-airway cough syndrome and lung cancer. Antibiotics within the first 21 days of pertussis infection can prevent transmission to others. The National Institute for Health and Care Excellence (NICE) Clinical Knowledge Summary recommends a macrolide antibiotic first-line, but only within the 3-week window (NICE, 2018). The cough is still likely to last up to 3 months (and known as the ‘100-day cough’ in China). There are no effective treatments to provide symptomatic relief, making measures to prevent spread even more important.

This case and the discussion offer important learning points:

Whooping cough causes persistent cough in adults