Primary Resistance of Mycobacterium Tuberculosis to Isoniazid, Streptomycin, Rifampin, and Ethambutol in Pulmonary Tuberculosis
Hassan Heidarnejad MD, Behrooz Nagili MD
Tabriz Tuberculosis Center, Tabriz University of Medical Sciences, Tabriz, Iran
Background-Paucity of information about primary
drug resistance in this region and the necessity of
obtaining information due to worldwide emergence of
multidrug resistance tuberculosis (MDR-TB) prompted this
study.
Methods-A
total of 165
specimens from cases with pulmonary tuberculosis were
selected in 3 consecutive years by the non-probable
convenience method. This sample included about 1/3 of all
sputum/washing-positive pulmonary tuberculosis (TB) cases
. Direct microscopy we used according to the
"International Union against Tuberculosis and Lung
Disease" (IUATLD) guideline; for culture, isolation
and sensitivity test we applied the WHO guideline in
order to compare our results with those of national and
international studies on primary drug resistance. Relapse
cases or patients with previous history of anti-TB
treatment and mycobacteria other than Mycobacterium
tuberculosis (including Mycobacterium bovis) were
excluded from the study by careful enquiry of records and
laboratory data.
Results-Seventeen
cases were excluded from the study and the remaining 148
had the clinical and laboratory criteria of primary drug
resistance. Mean age of the patients was 44.01±18.23 and
56% were males. All patients had clinicoradiological
findings of pulmonary tuberculosis. Single primary drug
resistance to isoniazid (INH) and streptomycin (SM) were
4.05 % and 8.78 % and total primary resistance were 7.43%
and 12.83 % respectively. Combined resistance to INH+SM
was seen in 3.38% of cases, and no resistance was
detected to rifampin (RMP) and ethambutol (ETB) amongst
new patients affected by Mycobacterium
tuberculosis. Resistance to RMP and ETB was
noticed only in patients with a previous history of
anti-TB therapy (secondary resistance) or in patients
with non-tuberculous mycobacteria.
Conclusion-In
this study which was conducted on patients with pulmonary
TB, the highest primary resistance was towards SM and INH
alone or to both of these drugs. There was no primary
resistance to RMP or ETB, and hence the possibility of
MDR-TB is negligible in our region.
Keywords • Mycobacterium tuberculosis • isoniazid • ethambutol • rifampi0n • streptomycin
Introduction
Drug resistance has been known since the discovery of the first anti-TB drug, streptomycin , in 1954 and the presence of resistant mutants in wild populations of mycobacteria has been well documented. Primary resistance is the resistance pattern seen in new patients, who have not been exposed to anti-TB drugs previously. Secondary resistance is the resistance pattern in patients with previous history of anti-TB treatment and is due to ineffective chemotherapy. Surveillance of the primary and secondary resistance patterns are important in assessing the quality of chemotherapy programs over several years and detecting errors in past treatments respectively.1-4 This has been performed for years in many countries. Unfortunately, due to selection bias and the variety of methods used in the isolation and sensitivity tests, old studies are not comparable.5-13 Scattered studies on drug resistance in Iran, mostly by the Pasteur Institute was not free of the above-mentioned surveillance errors.3 Because of the emergence of multidrug resistance tuberculosis (MDR-TB), especially after the HIV epidemic, surveillance of the drug resistance by using a single universal method with applicability even to countries with poor economy has been one of the WHO priorities in estimation of the situation all over the world.14 Our study is based on the WHO guidelines. Local facilities are utilized directly for assessing primary resistance and indirectly the quality control of the mycobacteriologic laboratory by comparing results with the national survey.
Materials and Methods
Specimens were obtained from patients with pulmonary tuberculosis, which were all diagnosed according to clinical and radiological findings. The specimens included sputum (83%), bronchial washes (20%), gastric aspirate (one case) and sinus pus (one case) and included a little more than 1/3 of all sputum/bronchial wash-positive cases. All these specimens were selected by the non-probable convenience method. The mean age and standard deviation (SD) of the patients was (44.01±18.23), among whom 56% were males. For direct microscopy we used the IUATLD guideline15 and for culture, strain isolation and sensitivity we applied the WHO/ IUATLD guideline16 for drug resistance surveillance with exclusion of the reference laboratory. Instead, some of our specimens were sent blindly to the National Tuberculosis Center, Tehran, for double check with the results of national drug resistance sponsored by WHO. The culture medium was prepared with local facilities and its quality was determined by the National Tuberculosis Laboratory, in Tehran. Critical concentration for isoniazid (INH), rifampicin (RMP), ethambutol (ETB), and streptomycin were 0.2, 40, 2, 40 mic/ml respectively. For interpretation of resistance we applied the proportion method. For isolation of mycobacteria we used the above-mentioned guideline with attention to colony type, pigmentation, niacin test, nitrate reduction test and TCH resistance test. Exact determination of non-tubeculous mycobacteria was not possible.
Results
A total of 165 specimens were studied, 56% of whom were males. The mean and standard deviation of their age was 44.01±18.23. Mycobacterium tuberculosis was isolated in 155 cases (148 new patients and 7 known cases) while non-tuberculosis mycobacteria including M. bovis were isolated in just 10 cases (8 of which were new cases).
The sensitivity pattern of all mycobacteria (primary and secondary resistance to Mycobacterium tuberculosis and non-tuberculosis) and primary resistance in new patients are shown in Tables 1 and 2 respectively. Regarding Mycobacterium tuberculosis, 5 cases were resistant to both isoniazid and streptomycin and one case was resistant to 3 drugs. In non-Mycobacterium tuberculosis, secondary resistance to all drugs was seen in one patient while the other had resistance to 3 drugs.
Discussion
Our study was performed with the WHO/IUATLD laboratory guidelines and shows major primary resistance to INH and SM. This is not surprising because these two drugs were introduced earlier than other drugs. Amount or resistance to INH and SM is something between the observed percentages in well-developed and under-developed countries. We can draw few explanations for absence of resistance to ETB and RMP. First of all, the number of the specimens is not enough to reach a firm conclusion about the resistance to ETB and RMP. Between the published series, resistance to these two drugs has been low or very low in comparision to INH or SM and surveillance of more specimens (300-600) is needed for detecting a low resistance rate.16 In collected data of 35 countries published by Pablos-Mendez14 the mean primary resistance to RMP and ETB was 1.8% and 1% respectively and this is in favor of our results. In the report of Pablos-Mendez the highest resistance to ETB and RMP were from Latvia, the Republic of Dominican, Thailand and Estonia and this is explainable both with HIV infection and disrupted TB control system.14,17 Second, in our study region, anti-TB drugs were not available for subscription by private physicians and this may contribute to good control of patients and prevention of treatment failure. Third, we can not absolutely rule out laboratory errors. Although, we possess no means for quality control of our laboratory by the WHO approved reference laboratories, but we had the opportunity for cross-checking of 22 specimens in the national drug resistance surveillance sponsored by the WHO. Results of this control have been depicted in Table 2.
As it is evident from Table 3, in 17 of 22 cases, there is complete concordance between our study and the national study. If we consider the clinical condition and laboratory results in patient1, 4 and 5 of Table 3, the correlation is better in the Tabriz study as compared to the national survey. Fourth, emergence of MDR-TB has a strong relation to HIV infection. Although all our patients were not screened for HIV, but random studies both in our patients and in TB patients originating from the general population of Tehran has revealed no evidence for HIV infection. But due to HIV epidemy in South-West Asia and problems of immigrants we should not ignore this major health-threat and reliance on directly observed therapy (DOT) is a key point for combating against TB in such situations.17 Finally, delicate attention to the medical history of the patients is
mandatory for surveillance of primary drug resistance. We have excluded 17 cases from the study due to previous anti-TB medication use or history of TB treatment. Resistance to all drugs including RMP and ETB is quite common in these patients and reluctance in history taking may contribute to a false positive increase in the prevalence of primary resistance.
In conclusion, our study shows a high primary resistance to SM and INH and absence or very low resistance to RMP and ETB. This correlates with a history of anti-TB medication use in our region. The first two drugs were introduced earlier than others. The prevalence of resistance to SM was highest in our study, hence we suggest replacement of this drug by ETB to obtain better results whenever possible. Reliance on DOT is also a major point in the prevention of resistance and for attaining successful results.
Acknowledgment
We hereby would like to thank S. Amini, D. Habibzadeh, and D. Tagavimand for their laboratory assistance; Dr Yamani, Dr Zabehi and Dr. Madadi from the Tabriz Blood Transfusion Organization for their assistance in the HIV test; Mrs Gorbani in typing the manuscript; and Tabriz University of Medical Sciences Research Affair for financial support of this research.
References