A total of 1,846 patients were enrolled during the study period. Among these, 605 (32.8%) did not have baseline DST results, either due to a nonviable sample (99.2%) or incomplete resistance data for both isoniazid and rifampin (0.8%). The remaining 1,241 (67.2%) patients constitute the cohort for analysis presented here.
Of these 1,241, 419 (33.8%) had baseline MDR TB, among whom 195 (46.5%) had never been treated for TB and 224 (53.5%) had a history of previous TB treatment. Eight patients had extensively drug-resistant TB; 1 was a medical student, 1 had received prior self-administered treatment, 2 had household contacts (1 was a pediatric patient and the other was an adult), and 4 were identified as suspected category I failures, i.e., failure of first-line treatment for new patients. Of these 8 case-patients, only 1 (who had received self-administered treatment) had completed previous treatment.
Descriptive characteristics of the cohort are shown in . Compared with patients with drug-susceptible TB, those with MDR TB were younger, more likely to be single, more educated, and less likely to have ever smoked. Clinically, they were less likely to have been tested by using the BACTEC-460 system and more likely to have hemoptysis. MDR TB patients and patients with drug-susceptible TB did not significantly differ with respect to their year of enrollment, gender, and history of TB treatment. Compared with patients with drug-susceptible TB, patients with monoresistant TB were younger and more likely to be single.
Demographic and clinical characteristics of patients with tuberculosis, by drug-resistance status, Lima, Peru, 2005–2008*
The most frequent risk factors prompting referral for DST among patients with new smear-positive TB were being adults with a household contact with known or suspected MDR TB (32.1%), diabetes mellitus (20.0%), and suspected category I failures (19.5%). Among previously treated patients with smear-positive TB, those with multiple (>2) treatments (43.2%), adult household contact (18.6%), default of category I treatment (16.8%), and previously self-administered treatment (14.9%) were most frequently referred for DST. Among all patients with smear-positive TB, a single risk factor was identified in 485 (43.54%) patients, whereas 382 (34.29%), 205 (18.40%), 38 (3.41%), and 4 (0.36%) had 2, 3, 4, and 5 risk factors, respectively (data not shown).
The prevalence of MDR TB in Peru in 2007 among all TB patients, previously treated TB patients, and new TB patients is shown in (21
). In this national surveillance report, 8.3% of all TB patients, 5.2% of new TB patients, and 24.2% of previously treated TB patients in Peru were estimated to have MDR TB (21
). Limiting surveillance data to the 2 districts where our cohort was enrolled, 12.4% of all TB patients, 9.9% of new TB patients, and 24.0% of previously treated TB patients had MDR TB (Ministerio de Salud, unpub. data). In our cohort of 1,241 subjects, 33.8% of all patients, 31.6% of new TB patients, and 35.8% of previously treated TB patients had MDR TB. Because national surveillance was conducted on smear-positive samples only, we compared the proportion of MDR TB among patients with smear-positive results in our cohort to prevalence of MDR TB from regional surveillance estimates. As shown in and , our cohort showed higher risk for MDR TB among new TB patients and previously treated TB patients.
Prevalence estimates of TB drug resistance from national and regional surveillance data, and proportion of drug resistance in study cohort, Lima, Peru, 2005–2008*
MDR TB among new smear-positive TB patients compared with regional surveillance prevalence estimates, by NTP risk group, Lima, Peru, 2005–2008*
MDR TB among previously treated smear-positive TB patients compared with regional surveillance prevalence estimates, by NTP risk group, Lima, Peru, 2005–2008*
When stratifying our cohort by risk group, we found that diabetes mellitus (16.8%), adult (33.5%) or child (53.9%) patients with household contacts with known or suspected MDR TB, and suspected category I failure, i.e., positive smear or culture during the second or third month of category I therapy (66.7%), were associated with significantly higher relative risks of MDR TB among patients with new smear-positive TB, when compared with regional surveillance prevalence estimates. Among the 18 patients with diabetes and new smear-positive MDR TB, 10 (55.6%) had 2 risk factors for MDR TB at the time of enrollment. Of these, 5 (27.8%) had suspected category I failure, 4 (22.2%) were adults with a household contact, and 1 (5.6%) had confirmed category I failure. Breslow-Day tests for homogeneity indicated that the effect of adult household contact on the odds of MDR TB is modified by diabetes (p<0.0001), and that the effect of suspected category I failure on the odds of MDR TB is modified by diabetes (p = 0.0113). One patient with new smear-positive TB was suspected of failing category II treatment (i.e., positive smear or culture during the second or third month of category II therapy); this same patient met the risk group criteria for adult household contact and private or self-administered treatment. Among previously treated patients with smear-positive TB, the following factors were significantly associated with a higher relative risk for MDR TB, compared with regional surveillance prevalence estimates: adult household contact (51.4%), failure of category I treatment (73.3%), early relapse after category I treatment (40.0%), suspected (84.6%) or confirmed (61.1%) failure of category II treatment, and history of >2 previous TB treatments (38.3%).