Epidemiology of Tuberculosis of the Central Nervous System in Children

Incidence and Prevalence

• 33% of world’s population infected: The W.H.O. estimates that one third of the world’s population, or 2 billion people, are infected by M. tuberculosis. An estimated 8.8 million new cases of TB were recorded in 2005 worldwide, with 7.4 million of these cases occurring in Asia or sub-Saharan Africa. A total of 1.6 million people died from TB, including 195,000 patients infected with HIV (1, 6, 8).
• 1 million new cases/year in children: Of the 9 million annual cases of TB, the W.H.O. has estimated that approximately 1 million new cases (11%) and 400,000 deaths per year will occur in children younger than 15 years of age due to TB (1, 6, 9-11).
• 22 developing countries have 75% of cases: TB infection and disease among children are much more prevalent in developing countries, where resources for control are scarce. Of these childhood cases, 75% occur annually in 22 high-burden countries. It is estimated that in developing countries the annual risk of TB infection in children is 2.5% (9-11).
• Resistant to eradication: Hopes of totally controlling the disease have been dramatically dampened by a number of factors, which include the difficulty of developing an effective vaccine, the expensive and time-consuming diagnostic process, the necessity of many months of treatment, the increase in HIV-associated TB, and the emergence of drug-resistant cases in the 1980s (6, 7-11).

Age Distribution

• Incidence of TB increases with age: In populations with a low prevalence of TB, most cases of TB meningitis occur in adults. In the United States in 1996, case rates were low in infancy and decreased somewhat during early childhood. After the age of puberty, case rates showed a steady increase with age (1, 6, 10, 11). Younger children are more likely to develop meningeal, disseminated, or lymphatic TB, whereas adolescents more frequently present with pleural, genitourinary, or peritoneal disease.
• TB meningitis more common in young children: TB meningitis is more common in children aged 0–5 years than in any other age group. TB meningitis is uncommon, however, in children younger than 6 months and is almost unheard of in infants younger than 3 months because the causative pathology sequence takes at least 3 months to develop.
• TB unusual between 5 and 14 years: Children between 5 and 14 years of age have the lowest rates of TB in virtually every population. Children in this age range are rarely a source of infection to others. TB rates begin to increase again in late childhood and adolescence, particularly for girls. Poverty and socio-economic reasons have been cited as the most common causes for delay in seeking health care for women and the higher incidence (1).

Sex Predilection

• Equal: The gender ratio for TB in children is ~1:1 in contrast to adults for whom the male-to-female ratio is approximately 2:1.

Geographic Distribution

• Majority of cases in developing countries: TB remains a worldwide burden and is the seventh leading cause of death and disability, with most new active cases occurring in developing countries. In 80% of new cases, demographic factors such as poverty, crowding, malnutrition, and a compromised immune system play a major role in the worldwide epidemic, while the remaining 20% of cases are associated with HIV in sub-Saharan Africa. About 80% of the population in many Asian and African countries test positive in tuberculin tests, while only 5–10% of the US population test positive (1, 6, 11). In 2007, the country with the highest estimated incidence rate of TB was Swaziland, with 1,200 cases per 100,000 people. India had the largest total incidence, with an estimated 2.0 million new cases (1, 6, 14).
• Urban locations in developed world: In developed countries, TB is less common and is found mainly in urban areas. Rates per 100,000 people in different areas of the world in 2010 were as follows: globally, 178; Africa, 332; the Americas, 36; Eastern Mediterranean, 173; Europe, 63; Southeast Asia, 278; and Western Pacific, 139. In the U.S., Canada, and Australia, TB is many times more common among the aboriginal peoples, especially in remote areas (1, 6, 14).  

Risk Factors

• Age: Children are more at risk than are adults.
• Malnutrition: Malnutrition increases the risk for contracting TB in children as does recent measles (9-12).
• Disease prevalence: If TB is prevalent in the community, then an individual is at increased risk (11).
• Exposure: Exposure to someone who has, or is suspected to have, infectious TB is a risk factor, as is contact with an individual who has been in prison, the homeless, HIV-infected individuals, drug users, migrant farm workers, and nursing home residents (12,13).

Relationships to Other Disease States and Syndromes

• HIV: There is an increase in coinfection with TB for individuals who are HIV positive. It is estimated that one-third of the 40 million people living with HIV/AIDS worldwide are coinfected with TB. People with HIV are up to 50 times more likely to develop TB in a given year than are HIV-negative people. An estimated 11–13% of incident cases of TB were HIV-positive (14, 15).
• Malignancies: The use of immunosuppressive chemotherapeutic agents in patients with malignancies increases the risk for becoming infected with TB (12, 13).