PREDICTING
TUBERCULOSIS CASELOAD WITH THE ANNUAL RISK OF TB INFECTION IN CAMBODIA,
1995-1996
Norval PY1, Roustit C2, Kong Kim
San2
1 WHO, Phnom Penh Cambodia, 2 National
Tuberculosis Program, Ministry of Health, Phnom-Penh, Cambodia
Background: Tuberculosis (TB) surveys were
conducted twice in Phnom Penh in 1995 and 1996 and once in the country in
1995 to estimate the prevalence and the annual risk of tuberculosis
infection (ARTI).
Methods: Representative sample in
schoolchildren aged 5 to 9 in Phnom Penh and in all provinces, with the
exception of the unsafe zones. Intra-dermal tuberculin test PPD
RT23/tween80 1TU was applied to 2861 children with no BCG scar in 1995 and
PPD RT23/Tween 80 2 TU to 2371 children with no BCG scar in 1996. Based on
tuberculinic surveys, it has been possible to calculate the prevalence
rate.
Results: The ARTI is estimated to be 1.2%
in Phnom Penh and 1.1% in Cambodia in 1995 with 1 TU and 7 mm cut-off
point. In 1996 with 2 TU and 8 mm cut-off point ARTI in Phnom Penh is 1.5%.
Mirror image techniques confirm results. The difference between 1995 and
1996 in Phnom Penh is not statistically significant (p>0.05).
Conclusion: The ARTI is equally distributed in cities and rural areas of
Cambodia. Results with RT23 1TU and 2 TU are similar. The prevalence of
infection has declined 1.9% per year from 1955 to 1995 in Phnom Penh and in
the rest of the country. Case notification and estimates for smear positive
cases in Cambodia in 1995 is respectively 118 and 251 per 100 000 inhabitant
corresponding to 2.3 to 4.8 times the ARTI estimates. Predicting the number
of TB cases based on ARTI is not possible in Cambodia and should be
replaced by prevalence survey.