EPIDEMIOLOGY <<Back
 
 
012
PREVALENCE, FATE, SOURCE AND INFECTIVITY OF RESISTANT IN MYCOBACTERIUM TUBERCULOSIS
Raj Narain, P Chandrasekhar, Pyare Lal and RA Satyanarayanachar: Proceed Natl TB & Chest Dis Workers’ Conf, Hyderabad, 1967, 37-51.

The material on resistant strains of mycobacterium tuberculosis is derived from the longitudinal survey conducted from 1961-68 in a random sample of 133 villages of 3 taluks of Bangalore district. About 54,000 persons aged five years or more were surveyed 3 times at an interval of 18 months, two samples of sputum were collected from persons whose chest X-rays were judged to have abnormal shadows. The sputum specimens were examined by direct smear and culture and sensitivity tests were performed.

An attempt is made to study prevalence, fate, source and infectivity of resistant mycobacterium tuberculosis in three rounds. PREVALENCE: In the 3 rounds, 199, 194 and 176 cases respectively yielded positive cultures; Of them, 30, 36 and 53 cases were having resistant strains. At round III, the number of culture positive cases has not fallen significantly, but the number of strains resistant to INH alone has sharply increased (13, 18 & 35). Both findings are likely to be due to the treatment with INH alone offered at round II and also due to the fact that treatment was taken very irregularly. FATE: Over period of 3 years, of the cases with INH resistant strains, more than 1/3rd were dead, 1/4th continued to remain positive and resistant, and 1/4th became culture negative. Whereas, of the cases with strains sensitive to INH, less than 1/3rd were dead, 1/3rd became negative and the remaining were positive, 1/2 with sensitive strains and 1/2 with resistant strains. SOURCE OF CASES: The prevalence of cases with resistant strains at any one round is not due to the persistence of such cases from previous rounds but by development of new cases with such strains at each round. INFECTIVITY: The incidence of infection among contacts with sensitive strain was significantly more than among the contacts of cases with resistant strain. It is inferred that the infectivity of sensitive strains is more than that of the resistant strains.

KEY WORDS: M.TUBERCULOSIS, SENSITIVE STRAINS, RESISTANT STRAINS, CASE, FATE, PREVALENCE, INFECTIVITY.

014
RESISTANT AND SENSITIVE STRAINS OF MYCOBACTERIUM TUBERCULOSIS FOUND IN REPEATED SURVEYS AMONG A SOUTH INDIAN RURAL POPULATION
Raj Narain, P Chandrasekhar, RA Satyanarayanachar & Pyare Lal: Bull WHO 1968, 39, 681-99.

The degree of the risk of infection and disease in man from drug resistant strains of mycobacterium tuberculosis is not clear. An increase in the prevalence of primary resistance indicates the extent of such risk while an increase of secondary or acquired resistance could be considered as a problem of the individual patient and may reflect limitations of his treatment.

The present report describes the prevalence of strains with acquired or primary resistance or of sensitive strains found in 3 successive surveys in a sizable random sample of village in a south Indian district. Changes in the status of cases with such strains from one survey to another and their infectivity among household contacts are also described. The prevalence of tuberculosis infection among household contacts of cases with acquired resistance to isoniazid was significantly higher than those with primary resistance or with sensitive culture. This was probably due to the longer duration of sputum positivity of isoniazid resistant strains at the time of diagnosis. But infectivity as judged by the incidence of new infection among household contacts was generally less for cases with acquired or primary resistance than for cases with sensitive cultures, though the difference observed was not statistically significant. A large number of culture positive cases especially those with primary resistance had no radiological evidence of active pulmonary tuberculosis. The prevalence of primary resistance was high in certain categories of cases and the differences between cases with primary resistance and those with acquired resistance were many and large. It was suggested that this could be due to the primary resistant cultures being those of atypical mycobacteria, despite positivity in the niacin test. There was a significant increase in the number of cases with acquired resistance to isoniazid at the third survey owing to the irregular treatment and supply of INH alone after the second round. The prevalence of primary resistance at the three rounds was almost the same.

KEY WORDS: DRUG RESISTANCE, M.TUBERCULOSIS, RURAL POPULATION, INFECTIVITY, SURVEY.
 

 
  BCG  
 
 
132
BCG VACCINATION INDURATION SIZE AS AN INDICATOR OF INFECTION WITH MYCOBACTERIUM TUBERCULOSIS
GD Gothi, SS Nair, Kul Bhushan, GVJ Baily & GE Rupert Samuel: Indian J TB 1974, 21, 145-51.

After the introduction of direct BCG vaccination, assessment of post-vaccination allergy and information about prevalence of infection could not be obtained. Few methods were tested i.e., i) retesting of persons with 0-13 mm reaction at site of vaccination on 4th day of vaccination, ii) retesting of all vaccinated persons of age 0-10 years. It is not only necessary to find out the size of BCG lesion that could separate them but also the day after vaccination on which the tuberculin reaction size best correlates with the BCG vaccination size. With this in view, two studies with regard to direct BCG vaccination done in India have been examined further. In Study I, 816 eligible persons were tested with 1 TU RT 23 read on 3rd day and vaccinated with either Indian or Danish vaccine. The vaccination lesions were examined on the 3rd, 6th and 90th day of vaccination. On the 90th day post-vaccination tuberculin test was done and read on 3rd day. In Study II, a total of 691 who had no previous BCG scar were simultaneously tuberculin tested with 1 TU RT 23 and vaccinated with either Indian or Danish vaccine. The BCG lesions were examined every day and on 39th and 90th day.

The correlation of pre-vaccination tuberculin test and BCG lesion size showe d that sixth day in first study and fifth day in second study was the highest. Tuberculin reaction size of 10 mm or more correlated well with 14 mm or more induration size of BCG in classifying the persons as infected and non-infected. Correlation between the size of BCG scar at 3 months and size of pre-vaccination tuberculin reaction was poor. Considering the two studies together vaccination induration of 14 mm or more on 5th or 6th day appears to be the best criterion for demarcating the infected from non-infected. Some other choices are 12 or 14 mm levels on 2nd day, 10 and 12 mm levels on 5th day and 10 mm levels on 8th day seems to be nearly as good and operationally useful.

A BCG Vaccination induration size of 14 mm and above between 5th and 6th day of vaccination, for all practical purposes may be considered satisfactory for demarcating persons infected with M.tuberculosis from those non-infected. It can be concluded that estimation of prevalence of infection, when BCG vaccination is given to all without prior tuberculin testing, can be made on the basis of BCG vaccination induration size of 14 mm or more.

KEY WORDS: BCG VACCINATION, M.TUBERCULOSIS, INFECTION, TUBERCULIN INDURATION, RURAL POPULATION.
 

 
  BACTERIOLOGY  
 
 
137
INVITRO STUDY ON SENSITIVITY OF TUBERCLE BACILLI TO THIOACETAZONE (TB1)
K Padmanabha Rao, SS Nair, N Naganathan & G Ramanatha Rao: Indian J TB 1966, 13, 147-57.

This report is based on the study of 735 cultures of tubercle bacilli identified as human type. Sputum specimens were collected from patients attending the Lady Willingdon Tuberculosis Demonstration and Training Centre (LWTDTC), Bangalore, and from the mass Case-finding studies in semi-urban areas. Drug sensitivity tests for streptomycin, isoniazid, PAS and thioacetazone with different drug concentrations, different size of inoculum and for various length of incubation were carried out.

No difference was observed in the duration of growth between sensitive and resitant cultures in their first appearance on primary diagnostic cultures or sub-cultures on drug free slopes when innoculated with standard suspension. The primary cultures took about 3 weeks and sub-cultures 2 weeks to grow on drug free media. Large sensitive bacillary population required higher concentration of thioacetazone to inhibit the growth, suggesting standardization of inoculum size for sensitivity tests. Prolonged incubation period on drug slopes showed profound influence on the level of drug inhibiting concentration of thioacetazone; with the increase in incubation period, fall in growth of sensitive culture was not observed even on high drug concentration. The reproducibility of this observation on duplicate specimens from the same patients after shorter intervals excluded the possibility of experimental error. A reduction in the inhibition of growth of sensitive organisms on drug media with time is presumed to be due to either deterioration of the drugs in the media or due to adaptation by the micro-organisms. Because of the decrease in inhibition of growth, even sensitive organisms may be classified as resistant if reading of culture for drug sensitivity is prolonged beyond 3 weeks of the inoculation period. It is suggested that a standard inoculum size and a maximum limit of 3 weeks incubation period should be adopted for finding out sensitivity to thioacetazone. Cultures classified as sensitive to the three first line drugs or resistant to one or more, showed no difference in the pattern of sensitivity to thioacetazone.

KEY WORDS: INVITRO DRUG SENSITIVITY, M.TUBERCULOSIS, THIOACETAZONE.

147
UTILITY OF PYRUVATE MEDIUM FOR ISOLATION OF M.BOVIS AND M.TUBERCULOSIS RESISTANT TO INH
N Naganathan & R Rajalakshmi: Indian J Med Res 1977, 66, 556-61.

A study was conducted to evaluate the usefulness of pyruvate medium for isolation of M.bovis from human material and additional yield of M. tuberculosis resistant to INH. Specimens from both rural and urban populations were included for this study in order to understand the problem in both the situations. There were two studies in progress at the National Tuberculosis Institute when pyruvate media slopes were introduced for culture purpose. One study was an epidemiological survey; 2518 sputum specimens received from 51 villages covering a population of about 32,300 were used. The specimens were collected from persons aged 5 years and above showing abnormal shadow on X-ray. The other study was conducted in collaboration with the State Tuberculosis Centre, Bangalore; 1204 sputum specimens were received from out patients attending the centre. In addition to LJ medium, pyruvate medium was used for isolation purposes. Identification and sensitivity tests were done on positive cultures as per routine. In all, 129 cultures of tubercle bacilli were isolated from 2118 specimens belonging to study 1 and 398 from 1204 specimens belonging to study 2. The number of cultures contaminated were 253 and 35 respectively. No M.bovis was isolated in either study. There were 24 and 23 cultures resistant to INH among those isolated from LJ and pyruvate medium respectively. Thus, no increase was observed in the isolation of INH resistant strains using pyruvate medium.

Hence, no benefit was derived by using this medium over and above what was obtained from plain Lowenstein Jensen medium in both the situations.

KEY WORDS: PYRUVATE MEDIUM, LJ MEDIUM, M.TUBERCULOSIS, DRUG RESISTANCE, M.BOVIS, RURAL POPULATION, URBAN POPULATION.

150
VIRULENCE OF TUBERCLE BACILLI ISOLATED FROM PATIENTS WITH TUBERCULOSIS IN BANGALORE, INDIA
N Naganathan, B Mahadev, VK Challu, R Rajalakshmi, Bharathi Jones DW Smith: Tubercle 1986, 67, 261-67.

Studies from Madras had shown that the strain of M.tuberculosis isolated from south India were low virulent to guineapigs. The relationship between virulence in guineapigs and pathogenesis in humans could not be established earlier. A study was conducted to investigate the relationship of virulence with the pathogenesis by comparing the virulence of isolates from pulmonary tuberculosis with that from patients with TB meningitis. The strains of bacilli were obtained from three different sources: a) Sputum from rural tuberculosis patients living near Bangalore city, b) sputum of TB patients living in the city and c) from Cerebrospinal fluid (CSF) of patients suffering from tuberculous meningitis and admitted in different institutions in Bangalore city. The specimens were processed by standard recommended procedures and cultured on Lowenstein Jensen medium. The identification of an isolate as M. tuberculosis was based on the niacin test. Albino Guinea pigs of both sexes (who were bred and raised at this Institute) were used for the tests. The virulence assay and the calculation of the root-index of the virulence (RIV) were carried out according to the Mitchison method.

1) As per the RIV method, virulence has been classified into low, moderate and high. The study showed that the percentages of cultures having isolates of low, moderate and high virulence, were the same as that of isolates obtained from patients in Madras, reported by Mitchison et al., in 1960. 2) The distribution of the RIV of virulence of isolates from patients living in the city of Bangalore was significantly different (p < 0.05) from that of isolates from patients living in rural Bangalore. 3) The number of cultures classified as high virulent were significantly greater in isolates from patients with tuberculous meningitis compared with those from patients with pulmonary tuberculosis. However, 36% of the isolates from the meningitis group were of low virulence.

KEY WORDS: M.TUBERCULOSIS, VIRULENCE, RURAL PATIENTS, URBAN PATIENTS.

153
EFFECT OF CARBON DIOXIDE ON THE PRIMARY ISOLATION OF MYCOBACTERIA
MM Chauhan, TR Sreenivas & K Chaudhuri: Indian J TB 1991, 38, 81-85.

The stimulatory effect of carbon dioxide (CO2) on the growth of tubercle bacilli was reported by a few authors. A study was done to see the effect of CO2 on primary isolation of mycobacteria on Lowenstein Jensen medium in terms of (1) positivity rate (2) improvement in the rate of growth in cultures and (3) contamination rate.

One thousand and five clinical specimens were inoculated, after processing by modified Petroff's method, onto LJ medium and incubated with or without addition of 10% of carbon dioxide. Of the total positive cultures, 30.8% grew only under 10% carbon dioxide and in 58.3% growth was first seen in that atmosphere. The results of this study show that (1) 10% carbon dioxide increases the yield of mycobacteria in primary culture (2) it stimulates the temporal growth rate resulting in reduction of lag period by one week (3) the increase in yield is largely from smear negative specimens and (4) there is no significant increase in the contamination rate to offset the stimulating effect on mycobacterial growth.

KEY WORDS: M.TUBERCULOSIS, CARBONDIOXIDE, GROWTH STIMULATION.
 
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