Key learning points

  • Tuberculosis (TB) should be suspected in patients with relevant clinical symptoms (cough longer than two to three weeks duration, lymphadenopathy, fevers, night sweats, unexplained weight loss), particularly if they have epidemiological or social risk factors 
  • Appropriate samples from the body site where TB is suspected should be sent for TB testing
  • TB is spread by droplet infection; consider timely infection control measures if the patient has suspected pulmonary TB

Introduction

Tuberculosis (TB) is caused by the bacteria from the Mycobacterium tuberculosis complex. Mycobacterium tuberculosis (MTB) is the cause of over 96% of cases and is acquired by inhaling droplets containing the bacteria which have been coughed out by a person with TB in their lungs or larynx. Mycobacterium bovis (around 1% of cases) is acquired by consuming unpasteurised dairy products.1

Active TB infection can involve any part of the body. In the UK, about 50% of cases involve the lungs.2 The second most common site is lymph nodes, particularly cervical lymph nodes. Spinal TB causes significant morbidity and should be suspected in at risk patients with persistent, often mid-thoracic, back pain.3 Young children are at highest risk of developing serious miliary or meningeal involvement with TB.

Risk groups

In the UK, more than three-quarters of TB cases are in patients born outside the UK. The highest TB rates are in those from the Indian subcontinent, sub-Saharan Africa and Eastern Europe.2 Other groups with high rates of TB are those with social risk factors such as homelessness, alcoholism, drug abuse and/or a prison history;4 or medical risk factors which cause reduced immunity, such as human immunodeficiency virus (HIV) infection, transplantation and/or immunosuppressive treatments, for example, anti-TNF alpha therapy.5 It is important to remember that anyone can get TB and delays in diagnosis are often longer in patients who do not fall into these risk groups, as the diagnosis may not be considered.2

Diagnosis

Gold standard for the diagnosis of TB is to culture the bacteria from a sample where the TB is thought to be active, for example, sputum (lungs), lymph nodes and spinal abscess. These samples can be taken by a range of health care professionals including GPs, physicians, interventional radiologists and surgeons. It is important that samples are sent to microbiology laboratories for TB investigation as they need to be processed in special TB liquid culture media. There are no blood tests for active TB.

Case presentation

A 30-year-old man from Eastern Europe presented to Accident & Emergency (A&E) with a cough for several weeks, night sweats and weight loss. He had received broad spectrum antibiotics from the GP.

His chest X-ray showed extensive consolidation with likely cavity formation and a small right pleural effusion. The differential diagnosis was community acquired pneumonia with parapneumonic effusion or pulmonary ± pleural TB.

He was isolated to a single room and an urgent, random sputum was sent for TB investigation. Acid fast bacilli (AFB) were seen on microscopy. A GeneXpert test was done on the sputum. This confirmed, within two hours of presentation, that he had infectious pulmonary TB that was unlikely to be multidrug-resistant TB (MDR-TB).

He was admitted as he lived in a hostel with communal spaces and it was assessed that it would be difficult for him to self-isolate. Standard quadruple TB treatment with rifampicin, isoniazid, pyrazinamide and ethambutol was started.6 His case was notified to Public Health. Following discharge two weeks later, when he was assessed to be a low infection risk, adherence to daily treatment was monitored by video observed therapy.7 He completed six months of treatment in line with NICE guidance6 and was assessed as cured with complete resolution of his symptoms, radiological improvement and confirmation of sputum microbiological conversion.

Discussion

This case shows the importance of awareness of TB and of obtaining samples for TB investigations. These not only confirm the diagnosis, but also guide the assessment of the patient’s infectiousness and the need for isolation and contact tracing, as well as the treatment length and regimen used.

The ability to see AFB under a microscope indicates that there are a lot of bacteria per millilitre of sputum and that the patient is likely to be more infectious than someone who has sputum smear negative pulmonary TB.  
Recent advances in molecular techniques are providing increasingly rapid confirmation of diagnosis and the resistance patterns of the MTB. GeneXpert is a rapid (<2 hour), cartridge-based benchtop system which detects MTB DNA sequences and rifampicin resistance-conferring mutations by polymerase chain reaction.8 The importance of diagnosing rifampicin resistant MTB early is that this highlights the possibility of MDR-TB, which is defined as resistance to, at a minimum, rifampicin and isoniazid. Since January 2018, whole genome sequencing (WGS) is being performed on all MTB isolates and provides relatively rapid information on complete MTB drug resistance patterns and has the potential of informing contact tracing and outbreak investigations.9

Dr Helen Booth is a consultant thoracic physician and honorary senior lecturer, University College London Hospitals and University College London

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