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The potential impact of new diagnostic tests on tuberculosis epidemics.

Dye C - Indian J. Med. Res. (2012)

Bottom Line: In this study we use mathematical modelling to explore the potential epidemiological impact of these new tests, with particular reference to India.New diagnostic tests for active TB will have a bigger impact sooner where: disease incidence is high and most cases are due to recent infection; advances in test technology (test sensitivity, specificity, etc.) are combined with early diagnosis; new tests have not only better technical specifications than current tests, but also compensate for the misuse of existing tests; health system delays are long compared with patient delays, assuming the former are more amenable to change.New diagnostic tests will certainly improve TB control, but the highest impact will be obtained by applying tests with higher sensitivity and specificity early in the infectious period.

View Article: PubMed Central - PubMed

Affiliation: HIV/AIDS, Tuberculosis, Malaria & Neglected Tropical Diseases Cluster, World Health Organization, Geneva, Switzerland. dyec@who.int

ABSTRACT

Background & objectives: New diagnostic tests for tuberculosis, especially those based on nucleic acid amplification, offer the possibility of early and accurate diagnosis of active TB. In this study we use mathematical modelling to explore the potential epidemiological impact of these new tests, with particular reference to India.

Methods: A behavioural model of patient-doctor interactions embedded in an epidemiological model of Mycobacterium tuberculosis transmission, linked to field data, was used to investigate the effects of early diagnosis in preventing future TB cases.

Results: New diagnostic tests for active TB will have a bigger impact sooner where: disease incidence is high and most cases are due to recent infection; advances in test technology (test sensitivity, specificity, etc.) are combined with early diagnosis; new tests have not only better technical specifications than current tests, but also compensate for the misuse of existing tests; health system delays are long compared with patient delays, assuming the former are more amenable to change.

Interpretation & conclusions: New diagnostic tests will certainly improve TB control, but the highest impact will be obtained by applying tests with higher sensitivity and specificity early in the infectious period. Refined behavioural and epidemiological models should be able to investigate the mechanisms by which early diagnosis could be achieved, in addition to the consequent epidemiological effects.

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A. The number of doctors seen by 1049 male and female patients in Bangalore (mode 3, range 1-7), as reported to the RNTCP. B. Cumulative duration of health system delays in relation to the number of doctors seen. The slope of the line indicates that each doctor seen adds 11.5 days to the diagnostic delay. C. Fit of model 1 (grey) to the total number of male and female patients (black), assuming a failure rate at each point (and survival to visit the next doctor), f, of 0.7. The alignment of black and grey bars indicates a good fit of the model to the data. Open bars show the distribution of the number of doctors seen if a new diagnostic procedure reduced f to 0.35. D. Fit (lower line) to the data (filled circles) in A and C, and the estimated total number of patients (open circles) in this setting in Bangalore. Data from the study by Pantoja et al15.
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Figure 2: A. The number of doctors seen by 1049 male and female patients in Bangalore (mode 3, range 1-7), as reported to the RNTCP. B. Cumulative duration of health system delays in relation to the number of doctors seen. The slope of the line indicates that each doctor seen adds 11.5 days to the diagnostic delay. C. Fit of model 1 (grey) to the total number of male and female patients (black), assuming a failure rate at each point (and survival to visit the next doctor), f, of 0.7. The alignment of black and grey bars indicates a good fit of the model to the data. Open bars show the distribution of the number of doctors seen if a new diagnostic procedure reduced f to 0.35. D. Fit (lower line) to the data (filled circles) in A and C, and the estimated total number of patients (open circles) in this setting in Bangalore. Data from the study by Pantoja et al15.

Mentions: Based on patient interviews, Fig. 2A shows the number of doctors seen by 1050 TB patients in Bangalore before being diagnosed by the RNTCP15. For both men and women, the number of contacts ranged from 1 to 7, with a mode of 3. This pattern of multiple contacts between patients and doctors is not unique to Bangalore or India, and is found elsewhere in the Middle East and Asia18. In Bangalore, each doctor seen added 11.5 days (S.D. 0.94) to the diagnostic delay (Fig. 2B).


The potential impact of new diagnostic tests on tuberculosis epidemics.

Dye C - Indian J. Med. Res. (2012)

A. The number of doctors seen by 1049 male and female patients in Bangalore (mode 3, range 1-7), as reported to the RNTCP. B. Cumulative duration of health system delays in relation to the number of doctors seen. The slope of the line indicates that each doctor seen adds 11.5 days to the diagnostic delay. C. Fit of model 1 (grey) to the total number of male and female patients (black), assuming a failure rate at each point (and survival to visit the next doctor), f, of 0.7. The alignment of black and grey bars indicates a good fit of the model to the data. Open bars show the distribution of the number of doctors seen if a new diagnostic procedure reduced f to 0.35. D. Fit (lower line) to the data (filled circles) in A and C, and the estimated total number of patients (open circles) in this setting in Bangalore. Data from the study by Pantoja et al15.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3401708&req=5

Figure 2: A. The number of doctors seen by 1049 male and female patients in Bangalore (mode 3, range 1-7), as reported to the RNTCP. B. Cumulative duration of health system delays in relation to the number of doctors seen. The slope of the line indicates that each doctor seen adds 11.5 days to the diagnostic delay. C. Fit of model 1 (grey) to the total number of male and female patients (black), assuming a failure rate at each point (and survival to visit the next doctor), f, of 0.7. The alignment of black and grey bars indicates a good fit of the model to the data. Open bars show the distribution of the number of doctors seen if a new diagnostic procedure reduced f to 0.35. D. Fit (lower line) to the data (filled circles) in A and C, and the estimated total number of patients (open circles) in this setting in Bangalore. Data from the study by Pantoja et al15.
Mentions: Based on patient interviews, Fig. 2A shows the number of doctors seen by 1050 TB patients in Bangalore before being diagnosed by the RNTCP15. For both men and women, the number of contacts ranged from 1 to 7, with a mode of 3. This pattern of multiple contacts between patients and doctors is not unique to Bangalore or India, and is found elsewhere in the Middle East and Asia18. In Bangalore, each doctor seen added 11.5 days (S.D. 0.94) to the diagnostic delay (Fig. 2B).

Bottom Line: In this study we use mathematical modelling to explore the potential epidemiological impact of these new tests, with particular reference to India.New diagnostic tests for active TB will have a bigger impact sooner where: disease incidence is high and most cases are due to recent infection; advances in test technology (test sensitivity, specificity, etc.) are combined with early diagnosis; new tests have not only better technical specifications than current tests, but also compensate for the misuse of existing tests; health system delays are long compared with patient delays, assuming the former are more amenable to change.New diagnostic tests will certainly improve TB control, but the highest impact will be obtained by applying tests with higher sensitivity and specificity early in the infectious period.

View Article: PubMed Central - PubMed

Affiliation: HIV/AIDS, Tuberculosis, Malaria & Neglected Tropical Diseases Cluster, World Health Organization, Geneva, Switzerland. dyec@who.int

ABSTRACT

Background & objectives: New diagnostic tests for tuberculosis, especially those based on nucleic acid amplification, offer the possibility of early and accurate diagnosis of active TB. In this study we use mathematical modelling to explore the potential epidemiological impact of these new tests, with particular reference to India.

Methods: A behavioural model of patient-doctor interactions embedded in an epidemiological model of Mycobacterium tuberculosis transmission, linked to field data, was used to investigate the effects of early diagnosis in preventing future TB cases.

Results: New diagnostic tests for active TB will have a bigger impact sooner where: disease incidence is high and most cases are due to recent infection; advances in test technology (test sensitivity, specificity, etc.) are combined with early diagnosis; new tests have not only better technical specifications than current tests, but also compensate for the misuse of existing tests; health system delays are long compared with patient delays, assuming the former are more amenable to change.

Interpretation & conclusions: New diagnostic tests will certainly improve TB control, but the highest impact will be obtained by applying tests with higher sensitivity and specificity early in the infectious period. Refined behavioural and epidemiological models should be able to investigate the mechanisms by which early diagnosis could be achieved, in addition to the consequent epidemiological effects.

Show MeSH
Related in: MedlinePlus