A baby with a cough

Discussion

Tuberculosis in children is a potentially life threathing disease that needs prompt diagnosis and treatment. It represents a sentinel event in the community, indicating recent transmission from an infectious adult (as in this case). In England the rate of tuberculosis among children aged under 5 has remained stable at about four per 100 000 since the year 2000,2 with incidence higher in people of Asian and African ethnicity. Most cases occur in large cities such as London, where there is overcrowding and more people of non-white ethnicity.

Several factors have contributed to the recent global resurgence in tuberculosis, including HIV infection, overcrowding, immigration, and easy international travel. In our patient the child’s ethnicity and recent exposure to an adult with chronic cough led to clinical suspicion of tuberculosis. The mode of spread is usually through droplets when infected people cough or sneeze. The most common cause is Mycobacterium tuberculosis; other causes include M bovis and M africanum.

Diagnostic tests include culture of induced sputum or gastric lavage. Sputum is induced by using nebulised saline or salbutamol to collect the sample, which is taken from the oropharynx by suction. Gastric lavage is performed in the early morning after an overnight fast and involves instillation of 10 ml of 0.9% saline and aspiration of 5-10 ml lavage fluid through a nasogastric tube for three consecutive days. Other useful investigations include tuberculin skin test (Mantoux); tests that measure cell mediated immune reactivity to M tuberculosis, such as QuantiFERON-TB Gold; and chest radiography.

The Mantoux test is performed by injecting 0.1 ml (2 units) of tuberculin purified protein derivative intradermally into the inner surface of the forearm. When placed correctly, the injection should produce a pale raised area of skin (a weal), 6-10 mm in diameter.3 The reaction, measured in millimetres of the induration, should be read between 48 and 72 hours after administration. The diameter of the indurated area should be measured across the forearm. Less than 6 mm indicates a negative result unless the patient is immunocompromised. More than 6 mm but less than 15 mm indicates hypersensitivity to tuberculin protein. More than 15 mm indicated the patient is strongly positive or strongly hypersensitive to tuberculin protein.4

QuantiFERON-TB Gold is a whole blood assay based on interferon gamma release with ESAT-6 and CFP-10 antigens. Sensitivity and specificity are comparable to those of tuberculin skin testing; however, a repeat reading is unnecessary. Results are reported as positive, negative, or indeterminate. The test has been recommended as a screening tool in situations in which the tuberculin skin test is likely to be less reliable—such as for children taking immunosuppressants or corticosteroids—or to detect latent tuberculosis infection.1

In young infants it is common for the bacilli to spread to other organs, such as the heart, brain, and kidneys, so investigations, such as echocardiography, computed tomography, and renal scan, are needed to exclude these infections.

Delay in the diagnosis of tuberculosis increases the risk of poor clinical outcomes, including death and transmission of tuberculosis to others.56 Understanding which factors influence delay is crucial for controlling tuberculosis—for example, age, ethnicity, place of birth, and sex.5 In this case, tuberculosis was suspected on the fourth day, when the parents mentioned that the baby had been looked after by his grandmother. Diagnosis of tuberculosis was confirmed on the ninth day, when M tuberculosis bacteria were found in the gastric lavage. The baby was started on antituberculous drugs and gradually improved.