Tuberculosis: the tip of the iceberg

In general, it is said that Mexico is in an epidemiologic transition to emphasize that the relative frequency of chronic diseases among the population is increasing. Thus, the attention given to subjects such as cancer, diabetes, obesity and its complications by clinicians, researchers, and health policy makers is increasing every day.

However, the concept of epidemiologic transition also means that the health problems characteristic of developing populations, such as infectious diseases, particularly tuberculosis, are not behind.

The tuberculosis mortality rate has greatly diminished in Mexico since 1990 and has remained low, which undoubtedly is an achievement of the health care services.¹ However, the incidence rate has remained practically the same for more than twenty years, which means that this disease has not yet been eradicated.¹ Tuberculosis still exists, and physicians in training are no longer frequently in contact with these patients. Therefore, it is difficult for them to become aware of the fact that tuberculosis is “the great imitator” and that the exception more than the rule is to find a patient “from the book.” This can be observed in the study by Vázquez-Rosales et al.,² which is presented in this issue of the Boletín Médico del Hospital Infantil de México. For example, fever, one of the more frequent signs of tuberculosis, was only present in only half of the reported cases. Even further, this percentage would probably be even lower if the sample was taken from the general population and not only from confirmed cases referred to the third level of attention. In other words, the study by Vázquez-Rosales et al.² depicts what probably would be the “tip of the iceberg” of an unsolved health problem.

Accordingly, paraclinical tests are far away from solving diagnosis incertitude. The tuberculin test, one of the more used screening tests, showed a sensitivity of only 50% in the study by Vázquez-Rosales et al.,² a percentage close to what has been reported by other authors.^3,4 Regarding the search for stained acid-fast bacillus, a sensibility of 29% was shown, which was a higher percentage than that previously reported.⁵ In contrast, a 10% of culture sensitivity was observed, compared with the 30 and 40% that has been reported.⁵ Moreover, although PCR and biopsy seem to have good sensitivity, according to Vázquez-Rosales et al.,² it must be taken into account that these tests were only performed on a subgroup of patients. Therefore, the results cannot be extrapolated to the tuberculosis patient in general.

Surprisingly, the unidentified source of infection in almost 90% of the cases is one of the most important data reported in this study.² As commented by the authors, this “…denotes the delay in the search and identification of infected adults, which in turn contributes to the continuous exposure of non-infected individuals in risk of developing TB, which finally indicates that the chain of transmission is still active…”, clearly including children.

Conflict of interest

The author declares no conflict of interest.