The present study demonstrated a high prevalence of drug resistance amongst pulmonary TB isolates of M. tuberculosis from north India. In newly diagnosed cases the resistance to any of the first line drugs was observed to be 26.4% to isoniazid, 9.9% to rifampicin, 14.9% to ethambutol, and 28.1% to streptomycin. This is in agreement with reports from different parts of the country showing high resistance to isoniazid (32.9%), rifampicin (11.8%), and streptomycin (14.9%), but in contrast with a few other studies reporting low resistance to the tune of 3.2%, 0.5%, and 4.8% to isoniazid, rifampicin, and streptomycin respectively . There was a high level of drug resistance in previously treated cases for any of the first line drugs i.e. 46.9% to isoniazid, 27.6% to rifampicin, 33.7% to ethambutol, and 34.7% to streptomycin. Other studies from India have also shown high resistance to isoniazid (47–87.1%) and rifampicin (12.6-80.6%) in previously treated cases; however, the number of isolates in most of the studies was small so the high resistance reported cannot be extrapolated to the whole country .
There were 39 cases of MDR-TB found in the study with an overall prevalence of 17.8% (39/219). In new cases a prevalence of 9.9% MDR-TB was observed which is higher than the WHO estimated prevalence of 2.1% cases of MDR-TB among the notified newly diagnosed pulmonary TB cases in India in 2010. However, the reports of prevalence of MDR-TB in newly diagnosed cases vary from 0.6 to 24% from different regions of the country [11–13]. Similarly, among the previously treated group multidrug resistance was seen to be 27.6%, which is higher than the WHO estimate of 15% MDR-TB in notified retreatment cases in India in 2010, though other studies from different regions of the country report MDR-TB varying from 11.8 to 47.1% [14–17]. The data of MDR-TB from other regions of the world ranges from 2.1%, 4.9%, and 12%, in newly diagnosed cases to 12%, 23%, and 37% in re-treatment cases in the Region of the Americas, Western Pacific Region, and European Region respectively . The wide range of resistance data from different parts of India indicates the lack of uniform surveillance methodologies across the country. Also, the sample size in most of the studies is small and do not reflect a wholesome picture of the resistance data. On the other hand, this difference in the resistance patterns may be true to some extent, considering the wide geographical and administrative divisions of the country reflecting the gaps in implementation of the national TB control programs; although this needs to be studied in large multi-centric surveillance studies using uniform methodologies to obtain the drug resistance data. The high prevalence in our study could be attributed to the fact that it was carried out at a tertiary care hospital where patients are being referred from different parts of north India. Surprisingly, we did not find any isolate which was XDR-TB though XDR-TB has been reported from India and other parts of the world [18–22].
Of the total 2100 cases, there was a seropositivity of 9.23% for HIV, while among the 219 patients with TB there were 20.1% seropositive cases. In our study, a higher prevalence of HIV in TB patients was found as compared to the WHO estimate of a prevalence of 9% of HIV in TB patients in India for 2010, which may possibly be due to clustering of referred cases at our tertiary care hospital. However, similar to our findings a few studies from other parts of the country have shown higher seroprevalence of HIV in TB approaching to 17% and 20.39% from Chennai and Pune respectively [23, 24]. There was a significantly higher number of MDR M. tuberculosis isolates in the HIV seropositive group i.e. 27.3%, as compared to 15.4% in HIV seronegative group with an odd’s ratio of 2.3 (95% CI, 1.000-5.350; p value, 0.05).
In the present study, a majority of the patients with TB were from a lower socioeconomic background (66.9%), however the prevalence of MDR-TB in these patients was found to be 19.5% which was not significantly different from the prevalence of 23.7% among the patients of upper socioeconomic status. This indicates that although TB is more common in poor patients, yet poverty was not a determining factor for the occurrence of MDR-TB, although the sample size was not sufficient to give this observation a statistical significance. In a recent study conducted in South India, Gupta et al. observed a significantly higher prevalence of pulmonary TB in labourers, followed by white-collar workers, retired and unemployed, household workers and students, however, they have not looked into drug resistance patterns in these patients . The increased incidence of pulmonary TB among socio-economically lower classes can be attributed to lower education level and poverty [26, 27], although the true prevalence of TB in poor sections of the society may be higher than estimated because such patients have limited access to hospital medical services and a high mortality rate .