The above situation indicate that the positive conversion rate after BCG vaccination in countryside was lower than that of city.
(3) Tuberculin Reaction Among Children With Pulmonary Tuberculosis
A total of 692 children pulmonary tuberculosis cases were detected in the survey and 527 (76.2%) of them had examined by PPD testing. 512 children had positive reaction (≧6mm) and the positive rate was 97.2%. Among them, 446 children had an induration ≧10mm; 299 children ≧15mm; 123 children ≧20mm and the positive rates were 84.6%, 56.7% and 23.3% respectively.
2. Infection Rate
(1) Rate of Tuberculosis Infection
Situation in the country: PPD testing was carried out among 122.005 children without BCG scar and history of BCG vaccination. The criteria for positive reaction as well as the positive rate was ≧6mm. The infection rates of different age groups were as follows: 0〜14 year-7.5%: 7 years-6.6%, (annual risk of infection. ARI-1.0%); 14 years-13.4% (ARI-1.0%). The infection rates of different age groups in 1979 survey were as follows: 0〜14 year-8.8%; 7 years-7.2%, (annual risk of infection, ARI-1.1 %); 14 years, 17.9% (ARI-1.4%). The annual reduction rates (ARR) of ARI for different age groups from 1979 to 1990 were as follows: 7 years-1.0%; 14 years-2.8%. The infection rate in children under 5 years old was higher than that of 1979. This situation may be attributed to that the children for PPD testing in this survey may included a certain amount of children who had inoculated with BCG vaccination but without scar formation and the history of BCG vaccination was also uncertain. As shown in Table 6,there was a peak on the curve of children infection, rate at 1〜4 years age group.
Situation in city and countryside: The infection rate of children under 14 years old in city (town) was 12.22%; it was higher than that of countryside (7.14%). The infection rates of 14 years old children in city (town) and countryside were 19.0% and 13.0% respectively.
(2) Calculation of Annual Risk of Infection
The annual risk of infection was calculated in accordance with the formula introduced by the Tuberculosis Surveillance Research Unit (TSRU) of the International Union Against Tuberculosis (IUAT). The criteria of tuberculosis infection was that a child has an induration ≧6mm of PPD testing but has no BCG scar and history of BCG vaccination. The annual reduction rate of annual risk of infection in children under 14 years old was 2%.
3. BCG Vaccination
(1) BCG Scar
A survey of BCG vaccination was carried out in all 928 investigation points. 394,096 children under 14 years old were examined. A total of 201,098 children had BCG scar and the BCG scar rate was thus 51.0%. The BCG scar rates of children in city, town and countryside were 88.7%, 58.9%, and 46.7% respectively. The scar rate in 0 year old children was 28.9% and the scar rates of children in various age groups above 1 year old were about 50%. The above fact indicated that the scar rate of children under 14 years old did not increase with the increase in age. The scar survey revealed that 10.8% of children with history of BCG vaccination but without BCG scar. The percentage in city was 5.2%, town 8.8%; countryside- 11.5%.
(2) BCG Scar Rate in Provinces, Municipalities and Regions
Among 19 provinces, municipalities and regions, Shanghai had the highest scar rate (97.5%) in children under 14 years old and Beijing (92.7%), Jiangsu (85.8%), Ningxia (80.9%) followed. Xizhuang had the lowest scar rate (16.4%) and Hainan (17.6%), Guizhou (19.5%), Henan (14.40k) followed.
(3) Positive rate of PPD testing among children with BCG scar
The positive rate of PPD testing among children under 14 years old was 36.2%. The positive rates in 1 year, 8 year and 14 years old children were 32.8%, 41.8% and 43.9% respectively. Two third of the children with BCG scar under 14 years old had a negative PPD reaction. The fact indicated that the post-vaccination positive conversion rate was not so high in a big amount of children. Among children under 14 years old, the positive rate of PPD testing gradually increased in the age groups above seven years. The fact could be attributed to following two reasons: i) BCG re-vaccination was carried out among school children: ii) the occurrence of tuberculous super-infection was increased among school children since they increased the contact with community.
? TUBEROULOSIS MORTALITY
The tuberculosis mortality survey was carried out at 928 investigation points in 29 provinces, municipalities and regions. The survey covered a population of 1,538,963. A total of 7,913 deaths occurred from various causes and the overall mortality was 514.2/100,000. 314 cases died of tuberculosis and the overall tuberculosis mortality was 20.1/100,000. Among these, 294 were died of pulmonary tuberculosis and the mortality of pulmonary tuberculosis was 19.1/100,000. The various weighted mortality were described in the following relevant paragraphs.
