Among the elderly population in Hong Kong, a spate of tuberculosis (TB) is worrying public-health officials. But these cases are not the result of recent infection; they signal the emergence of disease from an infection picked up decades ago. "Almost all recent cases in the elderly have arisen through reactivation of long-term latent infections rather than recent new infections," says Benjamin Cowling, an infectious disease epidemiologist at the University of Hong Kong's School of Public Health in China. Improved standards of living and public-health campaigns in most of the industrialized world dramatically reduced rates of TB during the first half of the twentieth century. But, unlike in the West, Hong Kong, Japan and Korea only began to get to grips with TB after the Second World War. So people who were first infected as children back in the 1940s and 50s - and who have shown no sign of TB for over 50 years -are succumbing to the disease as their immune systems weaken. "Given a high prevalence of latent TB in the elderly, and currently no strategies to stop reactivation," Cowling says, "it is difficult to foresee major changes in TB incidence in the coming years."
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