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Exposure to M. tuberculosis PowerPoint Presentation
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Exposure to M. tuberculosis

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Exposure to M. tuberculosis

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  1. Exposure to M. tuberculosis o Etiologic epidemiology o Descriptive epidemiology o Predictive epidemiology

  2. In just 30 years the median age of tuberculosis patients in Finland has moved from the generation of parents to that of grandparents. People preferentially socialize with peers of the same age, thus interactions are intra-generational. In the case of parents, the important interactions are both inter- and intra-generational. In Europe, it is largely the parents (not the grandparents) who take care of the youngest. In other societies this might differ. In any case, the age in which tuberculosis predominantly occurs, will have important repercussions on the risk of exposure for different population segments.

  3. Infection with M. tuberculosis o Etiologic epidemiology o Descriptive epidemiology o Predictive epidemiology

  4. Risk of Infection Given Exposure: Largely Exogenous Factors Particles Volume x Exposure time Particles: Volume: Exposure time: Production of infectious droplet nuclei Volume of air and ventilation Time of inhaling air with droplet nuclei

  5. Production of Infectious Droplets and Droplet Nuclei o Aerosolization o Site and form of disease

  6. Clearance of Air o Dispersion of bacilli o Survival of bacilli

  7. Extent of Contact o Proximity o Length of contact

  8. Risk of Infection Among Contacts as a Function of the Proximity of Contact

  9. Potential Transmitters of M. tuberculosis Persons who cough Persons with sputum positive for acid-fast bacilli Persons not on chemotherapy Persons just started on chemotherapy Persons with a poor response to chemotherapy

  10. 30 meters Surgery TB Amb District Hospital

  11. Advising the District Medical Officer The number of infectious particles (tubercle bacilli) expelled into the air in this environment must be considered far above the average encountered in other areas of the city. While all patients are on treatment, some have commenced treatment only recently. The volume of air into which these bacilli are expelled to is, however, infinite given a distance from the surgical ward of 30 meters (outdoors proximity matters). The survival of bacilli outdoors in East Africa is likely to be limited because of frequent sunshine. The length of exposure of surgical patients is by definition limited. The District Medical Officer might be advised that the risk assessment allows construction of the ambulatory as planned.

  12. Infection with M. tuberculosis o Etiologic epidemiology o Descriptive epidemiology o Predictive epidemiology

  13. Descriptive epidemiology of tuberculous infection o Methodological issues in determining prevalence of tuberculous infection o Prevalence of tuberculous infection

  14. Milestones in the History of Tuberculin 1890 1907 1909 1909 1910 1924 1926 1934 1950ies 1958-65 1965-95 Koch Old Tuberculin von Pirquet scratch test Moro patch test Mendel intradermal test Mantoux intradermal test Hastings no-lesion, reactor cattle Crawford heterologous antigens Seibert PPD-S WHO surveys US Navy recruit study Korea surveys

  15. Standardization of the Tuberculin Skin Test o Standardization of tuberculin o Standardization of administration o Standardization of reading

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  19. Sensitivity to M. intracellulare in the United States Edwards LB, et al. Am Rev Respir Dis 1969;99:(No 4, part 2):13

  20. Example 1: 90% Sensitivity 90% Specificity 40% Prevalence Example 1: 90% Sensitivity 90% Specificity 10% Prevalence Example for the Dependence of the Predictive Value of a Positive Test on the Prevalence Condition Test present absent total pos 360 60 420 neg 40 540 580 tot 400 600 1000 Condition Test present absent total pos 90 90 180 neg 10 810 820 tot 100 900 1000 Predictive value of a positive test: 360 / 420 = 86% Predictive value of a positive test: 90 / 180 = 50%