Prevalence of extensively drug-resistant tuberculosis among patients with multidrug-resistant tuberculosis: a retrospective hospital-based study.
Background & objective: Extensively drug-resistant tuberculosis
(XDR-TB) is a difficult-to-treat form of multidrug-resistant
tuberculosis (MDR-TB). High rates of XDR-TB have been reported from
India. We sought to ascertain the prevalence of XDR-TB among patients
with MDR-TB treated at a tertiary care centre in New Delhi, India.
Methods: Case records of patients treated for MDR-TB at the All India Institute of Medical Sciences hospital, New Delhi, between 1997 and 2003 were retrospectively reviewed. All patients underwent a pretreatment drug-susceptibility testing (DST) to first- as well as second-line drugs. XDR-TB was defined as TB caused by bacilli showing resistance to rifampicin and isoniazid in addition to any fluoroquinolone and to at least one of the three following injectable drugs: capreomycin, kanamycin, and amikacin.
Results: A total of 211 laboratory-confirmed cases of MDR-TB were reviewed. The mean age of the patients was 33 [+ or -] 12 yr. Fifty one (24%) patients were females. All patients were sero-negative for human immunodeficiency virus infection. Five of the 211 MDR-TB patients had XDR-TB. The prevalence of XDR-TB was 2.4 per cent among MDR-TB patients.
Interpretation & conclusion: Our results showed that XDR-TB was rare among patients with MDR-TB treated between 1997 and 2003 at our centre. Unreported selection bias might have been responsible for the high prevalence of XDR-TB reported in previous hospital-based studies from India.
Key words Drug resistance--extensively drug-resistant tuberculosis (XDR-TB)--India--multidrug-resistant tuberculosis (MDR-TB) tuberculosis
|Article Type:||Clinical report|
Drug resistance in microorganisms
Tuberculosis (Care and treatment)
HIV infection (Care and treatment)
HIV infection (Health aspects)
Rifampin (Health aspects)
Prevalence studies (Epidemiology)
Sharma, Surendra K.
Saha, Pradip K.
Mishra, Hemant K.
|Publication:||Name: Indian Journal of Medical Research Publisher: Indian Council of Medical Research Audience: Academic Format: Magazine/Journal Subject: Biological sciences; Health Copyright: COPYRIGHT 2009 Indian Council of Medical Research ISSN: 0971-5916|
|Issue:||Date: Oct, 2009 Source Volume: 130 Source Issue: 4|
|Topic:||Event Code: 310 Science & research|
|Geographic:||Geographic Scope: India Geographic Code: 9INDI India|
Multidrug-resistant tuberculosis (MDR-TB) and extensively
drug-resistant tuberculosis (XDR-TB) have emerged as significant threats
to global tuberculosis (TB) control. The magnitude of the problem is
evident from the fourth global report of the World Health Organization
(WHO) which reported data from 81 countries across the globe (1).
Currently, MDR-TB accounts for 5.3 per cent of all TB cases in the
world, with the prevalence among new and previously treated cases being
2.9 and 15.3 per cent respectively. This report also has data on XDR-TB
in which second-line drug susceptibility testing (DST) was carried out
on 4012 MDR-TB isolates from 35 countries; among these, 301 (7%) were
found to be extensively drug-resistant (1). As of June 2008, 49
countries have reported laboratory confirmed XDR-TB cases to the WHO
(2). The exact prevalence of XDR-TB in most regions of the world is
currently unknown. A few earlier hospital-based studies from India have
reported alarmingly high rates of XDR-TB among patients with MDR-TB
(3-5). However, our personal experience in treating a large number of
patients with MDR-TB is that XDR-TB would be uncommon in our setting. In
order to confirm this anecdotal observation, we formally set out to
ascertain the prevalence of XDR-TB among patients treated for MDR-TB at
a tertiary care centre in New Delhi.
Material & Methods
The case records of patients with MDR-TB treated, during the period from 1997 through 2003, at the All India Institute of Medical Sciences (AIIMS) hospital, New Delhi were retrospectively reviewed. AIIMS is a large, tertiary level teaching hospital located in northern India. Before the initiation of treatment for MDR-TB, all patients underwent mycobacterial culture and DST at the New Delhi Tuberculosis Centre Laboratory, New Delhi. This laboratory was a supranational reference laboratory of the WHO during the study period. Cultures were done on Lowenstein-Jensen (LJ) slopes by Petroff's method (6). Niacin test, catalase test and para-nitrobenzoic acid (PNB) test were used to identify the isolated mycobacteria. DST was carried out by the proportion method for first-line drugs and resistance ratio method for second-line drugs (7). The tested drugs and their critical concentrations (in [micro]g/ml) were as follows: isoniazid--0.2, rifampicin--40, pyrazinamide--100, ethambutol--2, streptomycin--4, kanamycin--64, ciprofloxacin--8, ofloxacin--8, ethionamide --320, cycloserine--160, para-aminosalicylic acid--4, thiacetazone--4, and clarithromycin--128. MDR-TB was defined as TB caused by bacilli showing resistance to at least isoniazid and rifampicin. XDR-TB was defined as TB caused by bacilli resistant to rifampicin and isoniazid in addition to any fluoroquinolone and at least one of the three injectable second-line drugs: capreomycin, kanamycin and amikacin (8). Human immunodeficiency virus (HIV) testing was carried out routinely in all patients.
Of the 211 patients with MDR-TB, 67.4 per cent came from various States outside Delhi and 32.6 per cent from within Delhi. Most (98%, n = 207) of these patients had a history of previous treatment for tuberculosis. Only four patients were naive to anti-tuberculous drugs. The mean age of the patients was 33 [+ or -] 12 yr; 51 (24%) patients were female. The mean body mass index was 17.3 [+ or -] 3.0 kg/[m.sup.2]. All patients tested negative for HIV infection. The resistance rates to various first and second-line drugs observed are shown in Table I. Of the 211 patients, 21 patients (10%) showed resistance to one of the fluoroquinolones and 14 (6.6%) showed resistance to the injectable agent, kanamycin. Five cases of XDR-TB were detected. Thus, the prevalence of XDR-TB among MDR-TB patients was 2.4 per cent. Among the five XDR-TB patients, two patients had a definite history of previous treatment with second-line drugs; the remaining three patients had multiple previous courses of anti-tuberculosis therapy which most likely included second-line agents, but no detailed records were available. Table II shows the characteristics of the patients with XDR-TB.
We found that XDR-TB was rare among patients treated for MDR-TB at our centre. Our findings do not support the earlier reports of frequent occurrence of XDR-TB in India. The reported prevalence of XDR-TB in these hospital-based studies varied from 7.4 33.3 per cent (Table III). However, a population-based study from southern India suggested a low prevalence of XDR-TB9; notably, DST was performed at a WHO-accredited laboratory in this study. Our findings are in consonance with such an observation. The high rates of XDR-TB observed in previous hospital-based studies might be due to referral bias. Moreover, the DST was not performed at quality-assured, accredited laboratories in any of these studies. HIV infection and local failure of the control programme could have also possibly contributed to varying rates of drug-resistant TB in these studies and so is the small number of patients included in some studies.
The discrepancy in findings between the present and an earlier study (5) from the same institution can be explained by the difference in the nature of the two studies. The previous study (5) was conducted in full-blown AIDS patients and therefore, the basic study population was different from the present study. Although the present study was also hospital-based, we found that XDR-TB was rare. Notwithstanding, in our study, the DST was performed at a supranational reference laboratory. Perhaps, this might be one of the reasons for the discordant observations.
Another interesting observation was that none of the patients with MDR-TB was HIV co-infected in the present study. This finding is in agreement with previous studies on drug-resistant TB that had shown that HIV infection is not more common among drug-resistant TB patients than in the general population (10-12), although there are studies which contradict this finding (13,14). Though there are extensive data on HIV prevalence in TB as a whole, there have been only a few studies on prevalence of HIV among MDR-TB patients from India. In a study conducted in Chennai, HIV seropositivity among MDR-TB patients was 4.42 per cent (15), which is comparable to rates of HIV observed among ordinary TB patients. It is possible that HIV co-infected patients with MDR-TB succumbed to the illness before they could be diagnosed.
There are certain limitations to the present study. First, due to its retrospective nature, the study may not truly reflect the current pattern of drug resistance. It is well known that drug resistance is a dynamic phenomenon that needs to be studied in real-time. Second, being a hospital-based study, the present observations cannot be extrapolated to the community settings. Nonetheless, the low prevalence of XDR-TB in this referral population is reassuring.
The present observation, however, should not lead to a state of complacency. Large-scale representative population-based data are urgently needed to find out the true prevalence of XDR-TB in the community. Periodic drug-resistance surveillance should become a part of the national TB control programmes. It is important to improve the laboratory infrastructure and establish a nationwide network of quality-assured laboratories capable of carrying out second-line DST. Second-line drugs must be used judiciously and cautiously by physicians at all levels of medical care. Irrational use of second-line drugs, like adding fluoroquinolones to a first-line regimen or a failing regimen, should be avoided. Future large-scale population-based prospective studies should throw light on the prevalence of XDR-TB in the community.
Conflicts of interest
We declare that we have no conflict of interest.
Received February 12, 2009
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Reprint requests: Prof. S.K. Sharma, Chief, Division of Pulmonary, Critical Care & Sleep Medicine, Head, Department of Medicine
All India Institute of Medical Sciences, Ansari Nagar, New Delhi 110 029, India
e-mail: firstname.lastname@example.org, email@example.com
Surendra K. Sharma, Ninoo George, Tamilarasu Kadhiravan, Pradip K. Saha, Hemant K. Mishra & Mahmud Hanif *
Department of Medicine, All India Institute of Medical Sciences & * New Delhi Tuberculosis Centre New Delhi, India
Table I. Resistance rates to various first-line and second-line drugs among MDR-TB patients * First-line drug Resistance Second-line Resistance rate (%) drug rate (%) Isoniazid 100 Kanamycin 6.6 Rifampicin 100 Ciprofloxacin 9.5 Pyrazinamide 8.1 Ofloxacin 9.0 Ethambutol 20.9 Sparfloxacin 4.8 Streptomycin 49.8 Cycloserine 4.3 Ethionamide 3.8 Clofazimine 1.9 PAS 2.4 Thiacetazone 8.7 * Note--206 patients were tested for thiacetazone, 209 patients for cycloserine, 209 patients for clofazimine, and 208 patients for sparfloxacin. Other drugs were tested in all 211 patients. PAS, para-aminosalicylic acid Table II. Characteristics of the patients with XDR-TB S.No. Age/Sex Body-mass index Previous Previous use (kg/[m.sup.2]) treatment of second-line for TB drugs 1 42 / Male 15.2 Yes N.A 66 40 / Male 15.4 Yes N.A 100 58 / Male 17.2 Yes N.A 142 25 / Male 16 Yes Yes 180 24 / Male 18 Yes Yes S.No. Type of TB Pattern of drug resistance 1 Pulmonary R, H, K, Of, Cip, Thi 66 Pulmonary R, H, S, K, Cip 100 Pulmonary R, H, E, S, K, Cip, Of, Spar, Thi, Clof, Cyc, Et, PAS 142 Pulmonary R, H, K, Cip, Of 180 Pulmonary R, H, S, K, Cip, Of Cip, ciprofloxacin; Clof, clofazimine; Cyc, cycloserine; E, ethambutol; Et, ethionamide; H, isoniazid; K, kanamycin; Of, ofloxacin; PAS, para-aminosalicylic acid; R, rifampicin; S, streptomycin; Spar, sparfloxacin; Thi, thiacetazone; N.A, Not available Table III. Published studies on the prevalence of XDR-TB in India Study Setting No. of MDR-TB patients Mondal et al (3) Tertiary care centre, Lucknow 68 Jain et al (4) Tertiary care centre, Mumbai 326 Singh et al (5) Tertiary care centre, New Delhi 12 Thomas et al (9) Field trial, Chennai 66 Present study Tertiary care centre, New Delhi 211 Study No. of HIV-infected Prevalence patients of XD n (%) Mondal et al (3) Not reported 5 (7.4) Jain et al (4) Not reported 36 (11) Singh et al (5) All HIV-infected 4 (33.3) Thomas et al (9) Not reported 1 (1.5) Present study All HIV-negative 5 (2.4) MDR-TB, multidrug-resistant tuberculosis; XDR-TB, extensively drug-resistant tuberculosis
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