What we learn in time of pestilence: that there are more things to admire in men than to despise (Albert Camus, The Plague (1947). New York: Vintage Books, 1991:308)

A consultant respiratory paediatrician sits down to watch the national news on a rare quiet evening after a busy winter viral season. The lead story reports that a child-care worker in the paediatrician’s home city has recently been diagnosed with active pulmonary tuberculosis (TB). The local public health department is initiating an investigation to determine the sources of the infection, and the implications for those exposed to the worker, including the children attending the crèche.

The consultant considers the situation—what is the likelihood some of these children are going to end up in her care? What are the factors that determine the likelihood of developing tuberculosis infection after exposure to an affected person? And what factors determine the progression from infection to active disease? An important consideration is the degree of infectiousness of the index case. Patients with cavitary pulmonary disease or laryngeal disease are more infectious as are those whose sputum is positive for acid-fast bacilli on direct microscopy. The duration and nature of contact the children have had with the child-care worker is important—close and prolonged contact is much higher risk. The physical environment, including ventilation and building layout, in which the contact took place can also be a determinant of transmission.1

The paediatrician knows children are particularly vulnerable to the development of TB disease following infection, and the younger the child, the higher the susceptibility and the more rapid the progression of disease: 50% of infected infants less than 1 year old will develop pulmonary or invasive disease, 20–30% of those aged 1–2 years, and 5% of those aged 2–5.2 Underlying illnesses in children causing immunosuppression …