|Year : 2016 | Volume
| Issue : 2 | Page : 89-93
Incremental yield of second sputum smear examination for diagnosis of tuberculosis patients at a tertiary care teaching hospital in Puducherry, India
Ramesh Chand Chauhan, Anil Jacob Purty, Abel Samuel, Zile Singh
Department of Community Medicine, Pondicherry Institute of Medical Sciences, Puducherry, India
|Date of Web Publication||24-May-2016|
Ramesh Chand Chauhan
Department of Community Medicine, Pondicherry Institute of Medical Sciences, Puducherry - 605 014
Source of Support: None, Conflict of Interest: None
Background and Objectives: The Revised National Tuberculosis Control Programme (RNTCP) guidelines recommend two sputum smear examinations for the diagnosis of tuberculosis (TB). This does not reduce the patient's inconvenience and laboratory workload. So, the present study was conducted to assess the contribution of second sputum smear examination for the diagnosis of TB. Materials and Methods: A retrospective record review of TB laboratory registers at a tertiary care medical college hospital in Puducherry, India was conducted from April 2009 to December 2012. Results: A total of 2,917 patients were recorded in the RNTCP laboratory registers during the study period. Of these, 2,869 (98.4%) patients had given sputum samples for diagnosis and 48 (1.6%) were follow-up cases on TB treatment. Among 2,869 TB suspects, 397 (13.8%) were acid-fast bacilli (AFB)-positive although 616 (21.5%) failed to submit their second sputum samples. Further, among 2,253 (78.5%) TB suspects who submitted two sputum samples, 361 (16.0%) were AFB-positive. Of these, 98.3%, 98.6%, and 96.9% were positive on the first, second, and both sputum smear examinations, respectively. The additional yield of the second sputum smear was 1.7%. Conclusions: The incremental yield of second smear examination is low; this indicates that single sputum smear examination is enough for the diagnosis of TB in tertiary health care settings.
Keywords: Incremental yield, Revised National Tuberculosis Control Programme (RNTCP), sputum examination, tuberculosis (TB)
|How to cite this article:|
Chauhan RC, Purty AJ, Samuel A, Singh Z. Incremental yield of second sputum smear examination for diagnosis of tuberculosis patients at a tertiary care teaching hospital in Puducherry, India. J Med Soc 2016;30:89-93
|How to cite this URL:|
Chauhan RC, Purty AJ, Samuel A, Singh Z. Incremental yield of second sputum smear examination for diagnosis of tuberculosis patients at a tertiary care teaching hospital in Puducherry, India. J Med Soc [serial online] 2016 [cited 2021 Apr 17];30:89-93. Available from: https://www.jmedsoc.org/text.asp?2016/30/2/89/182907
| Introduction|| |
Early and accurate diagnosis is critical to tuberculosis (TB) care and control.  The diagnosis of pulmonary tuberculosis (PTB) in low- and middle-income countries often relies on direct sputum smear microscopy for acid-fast bacilli (AFB). Although microscopy is less sensitive than culture, it has sufficient sensitivity to identify most infectious cases of PTB and is relatively simple for passive case-finding. , Diagnosis of smear-positive TB among TB suspects (any person with cough of 2 weeks or more) requires examining two sputum samples with one of them being a morning sputum sample. Any one sample positive out of the two is enough to declare a TB suspect as a smear-positive TB patient. 
Particularly in high TB burden countries such as India, the diagnosis recommendation is not always possible in practice for reasons such as heavy workload of technicians and patient-based irregularities.  The existing standard sputum microscopy procedure requires a TB suspect to give a spot sputum sample and another early morning sample, for which he/she has to return to the health facility on the next day. This burdens the TB suspect and hence, many TB suspects drop out during the diagnostic procedure and remain untreated in the community, providing more opportunities for transmission of the disease.  For this reason, the World Health Organization (WHO) issued a policy statement recommending that "countries that have implemented the current WHO policy for two-sample case-finding consider switching to same-day diagnosis, especially in settings where patients are likely to default from the diagnostic pathway. 
Although the detection of TB patients increases with the number of sputum samples examined and a majority of the TB patients are diagnosed by first sputum sample examination, , performing more sputum sample/smear examinations will put a burden on the health care system. Thus, there is an urgent need to explore the possibility of reducing the number of samples from two to one, taking into consideration the convenience of the patient and health care providers.
There are many studies  to assess the incremental yield due to second and third smear examinations when three smear examinations were recommended but no study was found to assess the additional yield of second sputum smear examination during current laboratory practices. In this study, we have analyzed the contribution of the two consecutive sputum smears for the detection of AFB and additional TB patients detected by examining second sputum smear at a tertiary care medical college hospital.
| Materials and methods|| |
This retrospective study was conducted through a record review of Revised National Tuberculosis Control Programme (RNTCP) laboratory registers.
Study setting and population
This study was conducted at a medical college hospital in Puducherry, India, which is implementing the RNTCP as per the national guidelines for more than the past 10 years. Patients usually visit many health care facilities before coming to the present hospital and a majority of them are sputum-negative PTB and extrapulmonary cases. A dedicated directly observed treatment-cum-microscopy center has already been established to provide TB diagnosis and treatment facilities at the study site. The microscopy center has a full-time laboratory technician and at present attending TB suspects who are required to give two sputum samples (first spot, second early morning) over 2 days but if the patients come from distant places, the second sample is collected on the same day. Since the inception of the RNTCP in the study area, quality assurance methods have been followed to ensure the quality of sputum AFB microscopy.
The study was approved by the RNTCP State Task Force, Puducherry, India. Individual patients' consents were deemed unnecessary as the data from the records were used. No personal identifiers were recorded in the electronic databases.
Data collection and analysis
We examined the AFB smear results of all the sputum samples received in the laboratory from April 1, 2009 to December 31, 2012. All the information available in the RNTCP laboratory registers  (age, sex, reason for examination, result of specimens 1 and 2) were recorded and entered into a prestructured format in Microsoft Excel. To minimize data entry errors, the data were entered twice by two persons. The data were analyzed using Statistical Package for the Social Sciences (SPSS) software (SPSS Statistics for Windows, Version 17.0. Chicago: SPSS Inc., Chicago, Illinois, USA). The proportion of patients diagnosed with single sputum sample and both sputum samples were calculated and chi-square test was applied to find the association of positive sputum smears with various factors; P value of <0.05 was considered to be significant.
| Results|| |
During the study period, a total of 2,917 patients were recorded in the RNTCP laboratory registers as having submitted their sputum samples. Of them, 2,869 (98.4%) patients had given sputum samples for diagnosis (total TB suspects) and 48 (1.6%) were follow-up cases on TB treatment [Figure 1].
|Figure 1 : Flow of patients subjected to sputum microscopy and their sputum smear results (n = 2917)|
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Among the TB suspects, more than two-third were males (68.6%) and a majority of them (74.8%) were in the economically productive years of their life. The mean age of TB suspects was 48.2 years ± 18.0 years (<1-93 years). A total of 5,122 sputum samples were submitted by 2,869 TB suspects and 616 (21.5%) failed to submit their second sputum samples for diagnosis. The failure to submit their second sputum samples was significantly higher among females (23.9%) and patients in the age group of 15-34 years (P value <0.05). More TB suspects coming from January to March had given only single sputum sample and their proportion increased from 2009 to 2012 [Table 1].
|Table 1: Characteristics of patients subjected to diagnostic sputum examination (n = 2,869)|
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Overall, 397 (13.8%) TB suspects were AFB-positive and among those who submitted only single sputum samples, 36 (5.8%) were positive. Among TB suspects who submitted two sputum samples, 361 (16.0%) were AFB-positive. Of these, 355 (98.3%) were positive on examination of the first sputum sample, 356 (98.6%) were positive on examination of the second sputum sample, and 350 (96.9%) were positive on examination of both sputum samples.
By performing the second sputum smear examination, an additional six (1.7%) cases were detected in those TB suspects who were sputum smear-negative on first smear examination (incremental yield). Further, to detect a new case of TB by second smear, 266 (6/2253) sputum smears are required to be examined [Table 2].
|Table 2: Smear positivity and incremental yield of second smear examination among TB suspects who submitted two sputum samples|
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| Discussion|| |
Medical college hospitals play an important role in the diagnosis of TB patients, and at the national level almost one-fourth of the new sputum-positive cases are diagnosed in medical colleges.  Most of them are usually referred for treatment to peripheral health institutions (PHIs). In the present study also, only a few (1.6%) TB suspects were examined for follow-up of treatment, which makes it clear that most of the patients diagnosed at medical colleges are referred for treatment to PHIs.
Similar to other health facilities, examination of sputum samples by microscopy is the main method used for diagnosis of TB in medical college hospitals in India. Performing second smear examination, apart from causing an increase in workload, puts an unnecessary burden on the patient, and may actually result in fewer cases being started on treatment considering the numbers that do not return after a first positive smear.  In the present study, among 616 patients who did not submit their second sputum samples, 36 (5.8%) were AFB-positive on first sputum smear. None of them collected sputum examination reports.
Among 2,253 TB suspects, who submitted two sputum samples, 361 (16%) were AFB-positive. Of these, 98.3% were positive on first sputum smear examination and an additional 1.7% of the patients were detected by the second smear examination. Hence, collecting second sputum sample and examining the smears does not seem to an efficient way of diagnosing the PTB (as there is only 1.7% additional yield of performing second sputum smear examination). Possibly, the additional TB cases, equal to those detected by second sputum sample could be identified by improving the quality of sputum collection and processing. Also, more than 98% of the TB patients were identified from the first sample only. Similar findings were reported by another study conducted in Turkey where 97% of the AFB-positive patients were detected from the first sputum sample and only an additional 3% were identified from the second sample examination.  Many past studies , to find the additional yield of 2 nd and 3 rd smear showed a higher yield with second smear examination but in the present study, the additional yield was very low. One of the possible reasons for low yield in the present study could be due to collection of the second sample on the same day in approximately 25% patients who were coming from distant places. Second, the characteristics of patients coming to a private tertiary care hospital may be different from those coming to the other RNTCP TB diagnostic facilities. Also, we are not sure about the quality of second sputum samples, as no comparison of first and second sputum samples was done.
In the present study, 21.5% of the TB suspects failed to submit the second sputum sample. Other studies also reported a high noncompliance where for a variety of reasons, up to 50% of the patients failed to return to provide a second sample or receive results. , This noncompliance could be mainly due to patient factors such as due to different disease severity at the time of diagnosis, distant place of residence, and long patient delay among TB suspects coming to medical college hospitals. Same-day sputum smear microscopy (where all samples are collected and the results are reported on first day) is as accurate as standard smear microscopy.  This procedure reduces the economic burden of an additional visit and thus, leads to improved compliance and lesser dropout rates during diagnosis.  But performing two smear examinations as conventional methods or same day microscopy does not reduce the laboratory workload.
Further, even in patients with cough of less than 2 weeks there may be an appreciable prevalence of TB.  Thus, the examination of one sputum sample for 1 week's cough could be an alternative for improving case-finding. When a maximum yield rather than efficiency or cost-effectiveness is valued, more sputum samples can be examined provided that ample manpower is available but in countries with limited human resources such as India, one sample, one smear, and same-day result could be tried to minimize the missing of cases, particularly in tertiary health care settings. Further, this study is the first of its kind to assess the incremental yield of second sputum sample when only two samples are recommended to be collected under the guidelines; further studies to explore the efficiency of 1 week's cough as suggestive of PTB with one sputum smear examination should be conducted.
The strategy of examining one smear for the diagnosis of TB is encouraging, and would reduce the workload of the technicians who can devote more time for proper sputum collection, processing and reading, and attending to other responsibilities. As the study was conducted in a single medical college only, it is recommended to assess the incremental yield from the TB diagnostic facilities of various levels in different settings, with varying patient load and with different ways of sputum processing and microscopic methods. Further, the guidelines for detection of PTB need to be revisited and other simple and quicker methods for the diagnosis of PTB should be explored. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines for reporting observational studies. 
| Conclusions|| |
The additional yield of second sputum smear examination is very low among TB suspects attending a medical college hospital and many of them are not coming to submit second sputum samples. Also, examining only single sputum smear is as good as two sputum smears on the same day and this lessens the burden on the health system. But the incremental yield for second sputum smear examination could vary in different settings and so it is important to conduct similar studies in various settings.
The authors would like to acknowledge the assistance and cooperation of Dr. Govindarajan S, State Tuberculosis Officer of Puducherry, India for supporting the implementation of RNTCP in the study hospital.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]
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