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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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Related in: MedlinePlus

Comparative impact of three interventions, singly and in combination, on (A) the average duration of infectiousness, and consequently (B) TB incidence through time. Interventions begin in 2010. Below the elimination threshold of 0.78 yr in A, R0 < 1 and TB will eventually be eliminated.
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Figure 5: Comparative impact of three interventions, singly and in combination, on (A) the average duration of infectiousness, and consequently (B) TB incidence through time. Interventions begin in 2010. Below the elimination threshold of 0.78 yr in A, R0 < 1 and TB will eventually be eliminated.

Mentions: We choose initial values of δ = 2 (patient delay of 0.5 yr), τ = 0.5 (50% test sensitivity) and κ = 0.7 (70% cure). Health system delays arise because τ and κ take values less than 1, but these delays are foreshortened by death from TB and other causes. The model is a device that puts different interventions in the same currency - the infectious period - so these can be compared. With these parameter values and others in the Table, the mean infectious period is 1/(δτκ + μ + μi) = 1.1 yr. The total duration of infectiousness is divided almost equally between patient and health system delays, and this duration becomes shorter when any of the control parameters (δ, τ, κ) increases in value. The basic case reproduction number of R0 = 1.4 in this example, is the product of the contact rate, β, the proportion of infected people that ever develops infectious TB, s[q + (1 - q)v/ (v + μ)], and the duration of infectiousness. Any reduction in the duration of infectiousness by a factor of more than 1-1/1.4, or 29 per cent (to 0.78 yr or less), will ensure that R0 < 1 and that TB is eventually eliminated (Fig. 4A).


The potential impact of new diagnostic tests on tuberculosis epidemics.

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

Comparative impact of three interventions, singly and in combination, on (A) the average duration of infectiousness, and consequently (B) TB incidence through time. Interventions begin in 2010. Below the elimination threshold of 0.78 yr in A, R0 < 1 and TB will eventually be eliminated.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Comparative impact of three interventions, singly and in combination, on (A) the average duration of infectiousness, and consequently (B) TB incidence through time. Interventions begin in 2010. Below the elimination threshold of 0.78 yr in A, R0 < 1 and TB will eventually be eliminated.
Mentions: We choose initial values of δ = 2 (patient delay of 0.5 yr), τ = 0.5 (50% test sensitivity) and κ = 0.7 (70% cure). Health system delays arise because τ and κ take values less than 1, but these delays are foreshortened by death from TB and other causes. The model is a device that puts different interventions in the same currency - the infectious period - so these can be compared. With these parameter values and others in the Table, the mean infectious period is 1/(δτκ + μ + μi) = 1.1 yr. The total duration of infectiousness is divided almost equally between patient and health system delays, and this duration becomes shorter when any of the control parameters (δ, τ, κ) increases in value. The basic case reproduction number of R0 = 1.4 in this example, is the product of the contact rate, β, the proportion of infected people that ever develops infectious TB, s[q + (1 - q)v/ (v + μ)], and the duration of infectiousness. Any reduction in the duration of infectiousness by a factor of more than 1-1/1.4, or 29 per cent (to 0.78 yr or less), will ensure that R0 < 1 and that TB is eventually eliminated (Fig. 4A).

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