Page 46 - Epidemiological studies on tuberculosis control and respiratory viruses

Chapter 7
However, the contribution of contact investigations to reduce the burden of disease in the population as a whole remains to be investigated. Although contacts with LTBI identified near the time of exposure are at substantial risk for the development of TB (30), all latently infected individuals, including those who acquired infection at a much earlier time, are at risk of reactivation. Most molecular epidemiological studies agreed that TB incidence among foreign-born in low-incidence countries is mainly the result of reactivation of infection acquired in country of origin (31), either in the first five years after migration (32) (33), or after extended periods of arrival (34) (35). These findings suggest low levels of transmission in low-incidence countries where most TB cases are foreign-born. Thus, even if assuming optimal contact tracing strategies and diagnostic algorithms, a large proportion of TB cases cannot be prevented by contact investigations, which aim to intervene shortly after recent transmission events have taken place. Therefore, TB control measures in low- incidence countries might benefit from shifting the focus to screening for LTBI among newly arrived immigrants and thereby achieve a significant reduction of TB rates in the population as a whole. It should be noted that the impact of immigration on the TB epidemiology in low-incidence countries is difficult to measure, among others due to incomplete strain collections and low levels of transmission (36). Some molecular epidemiological studies have suggested that some TB cases among foreign-born in low-incidence countries are the result of new infections acquired in the host country (37) (38). Therefore, it will be important to continue surveying recent transmission in low-incidence countries between foreign-born and the native population, as well as within the foreign-born communities, and adapt TB control strategies accordingly.
Clinical significance of respiratory viruses detected by RT-PCR in upper airways
Sensitive real-time polymerase chain reaction (RT-PCR) assays allow detection of a wide range of respiratory pathogens, but concerns have been raised regarding the clinical significance of respiratory viruses detected in the upper respiratory tract. PCR has not only increased viral detection in symptomatic but also in asymptomatic individuals (39) (40) (41) (42), which has made the interpretation of a positive PCR result in patients with respiratory illness challenging, and this can delay appropriate treatment initiation. Up to now, most etiological research has focused on patients, mostly children, seeking health care for acute respiratory illness, and therefore findings might not be representative of mild disease (42). Investigating respiratory
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