Abstract
In many countries with low to moderate tuberculosis (TB) incidence, cases have shifted to elderly persons. It is unclear, however, whether these cases are associated with recent Mycobacterium tuberculosis transmission or represent reactivation of past disease. During 2009–2015, we performed a population-based TB investigation in Yamagata Prefecture, Japan, using in-depth contact tracing and 24-loci variable-number tandem-repeat typing optimized for Beijing family M. tuberculosis strains. We analyzed 494 strains, of which 387 (78.3%) were derived from elderly patients. Recent transmission with an epidemiologic link was confirmed in 22 clusters (70 cases). In 17 (77.3%) clusters, the source patient was elderly; 11 (64.7%) of the 17 clusters occurred in a hospital or nursing home. In this setting, the increase in TB cases was associated with M. tuberculosis transmissions from elderly persons. Prevention of transmission in places where elderly persons gather will be an effective strategy for decreasing TB incidence among predominantly elderly populations.
Highlights
The World Health Organization End TB strategy [1] calls for every country, depending on their tuberculosis (TB) situation, to accelerate efforts designed to end TB
Our findings indicate that elderly persons must be included in TB prevention and control measures in countries with low to moderate incidence that have experienced a shifting of TB cases toward the elderly [1,22,23]
Our results suggest that elderly patients with TB are a source of TB spread involving younger persons
Summary
The World Health Organization End TB strategy [1] calls for every country, depending on their tuberculosis (TB) situation, to accelerate efforts designed to end TB. In Japan, 14.4 TB cases/100,000 population were reported in 2015. Given that the incidence of TB was high in Japan until the 1970s [3], the current elderly population is regarded as vulnerable to TB onset from reactivation of remotely acquired latent infection [4,5]. TB transmission among elderly populations has not been determined worldwide [6]. Variable-number tandem-repeat (VNTR) typing is a useful method for rapidly detecting TB infections caused by the same strain of Mycobacterium tuberculosis [7]; such cases might occur from recent transmission. A combination of VNTR typing and in-depth contact tracing has detected previously unrecognized recent TB transmission in various settings [8,9,10,11]. M. tuberculosis Transmission, Japan, 2009–2015 the Ethics Committees of Yamagata Prefectural Institute of Public Health
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