1. Philippe Glaziou Geneva, 12 October 2009
A new perspective on TB disease burden and TB control in Viet Nam Lessons from a prevalence survey
Philippe Glaziou
Geneva, 12 October 2009

2. The problem with case detection rates
CDR not directly measurable
Optimal TB surveillance systems capture almost all incident cases
If surveillance is suboptimal, then what is directly measurable?
Prevalence (survey)
Mortality (vital registration)
Diagnosed patients: inventory studies
Mapping of providers
Size of diagnosed but not notified TB population

3. High case detection and treatment success but no decline in notifications in Vietnam: Why?

4. Prevalence survey showed prevalence much higher than previously thought
Prevalence rate per 100,000
Prior estimate (WHO)
Survey, * [95% CI]
Smear (+) 86
145 [ ]
Bacteriologically confirmed
226 [ ]
*Source: Prof Sy. Report of the National TB Prevalence Survey in Vietnam,

5. Estimating the case detection rate from a prevalence measurement
CDR = N/P / (N/P + 1/d) [1] d denotes the average duration of disease
Duration: triangular distribution from 1 to 4 years, mode at 2 years (EV = 2.3)
Prevalence: normal distribution around point prevalence estimate from the survey, s.e. adjusted for sampling design
[1] Borgdorff M. New measurable indicator for tuberculosis case detection. EID 2004; 10(9):

6. Case detection rates in 2007

7. Chronic cough lacks sensitivity, importance of relapses
Only 53% of prevalent sputum smear positive cases reported chronic cough
22% of ss(+) cases previously treated for TB (8-month regimen used in past)
36% more than 2 years before
64% recently, 63% of them successfully
Sex ratio (M/F) = 4.5 (bacteriologically confirmed cases)

8. Private providers
8% of 326 suspects with history of TB treatment were treated in the private sector
PPM intervention project (HCMC) +18% notifications in PPM districts over 1 year (-1% in other HCMC districts)
Internal migrants moving to cities tend to access care from the private sector

9. In-depth analysis of surveillance data
Decline in notifications in
older age groups, increase in young adults

10. Lessons learned
Disease burden higher than previously thought: keep TB high on the political agenda
Notifications estimated to reflect trends in incidence, declining at an age standardized rate of -2%/yr, but increasing in yr-old group
Importance of accounting for changes in demographic structure
Large pool of unreported cases in private sector
PPM, link with hospitals
Electronic recording and reporting
Improve screening, expand active case finding

11. Conclusions
Prevalence surveys provide robust measurement of national coverage and impact of TB control
Combined with in-depth analysis of surveillance data, survey results help
understand and interpret epidemiological patterns and trends
update policies on TB screening and care
improve reporting
address the needs of at-risk populations