The terms environment and public health are interdependent, because both are determined by the interplay and integration of internal environment of man himself and the external environment which surrounds him. In the modern concept, disease is due to a disturbance in the delicate balance between man and his environment. Therefore, the environmental sanitation is the most important parameter that determines the public health of an area [1]. WHO has defined environmental sanitation as the control of all those factors in man’s physical environment which exercises or may exercise a deleterious effect on the physical development, health and survival.

The term environment implies all the external factors-living and non-living, material and non-material which surround man. Environment not only includes water, air and soil that form our ambience, but also the social and economic conditions under which we live. The key to man’s health lies largely in his environment. The study of diseases is really the study of man and his environment [2].

Communicable diseases are infectious or contagious diseases transmissible from an affected individual to another by direct contact with the affected individual or through the affected individual’s discharges or through vectors. Tuberculosis, an infection caused by Mycobacterium tuberculosis, is a worldwide pandemic, and the Centers for Disease Control and Prevention (CDC) state that one-third of the world's population is infected with the bacteria. In the majority of those infected, however, the infection remains latent, meaning that it does not progress to an active disease. Many factors affect whether tuberculosis becomes an active infection that can then result in one of more than 2 million deaths a year caused by this bacteria [3].

Symptoms of Tuberculosis depend on the part of the body where the bacilli are growing. Most favourite site of infection is the lungs but their infection may be of extra-pulmonary. Usual symptoms include a bad cough that lasts 3 weeks or longer, pain in the chest, coughing up blood or sputum (phlegm from deep inside the lungs), weakness or fatigue, weight loss, no appetite, chills, fever etc.

Tuberculosis is most prevalent in underdeveloped countries due to unsanitary living conditions, crowded living quarters and lower income levels.

The topography of the valley is heterogeneous having hills, wetlands and plain areas. The Barak-Surma-Kusiara river system passes through this valley. The valley is covered with a network of sluggish streams and saucer like depressions. Numerous hillocks stand all over the valley. The valley is also covered by hill ranges from North, East and South having vast tracts of forest land.

Climatic condition of the valley is characterized by high humidity to the extent of 96%. Average rainfall is as high as 2700-2800 mm and during recent past the minimum and maximum annual rainfalls have been recorded to be 2161 mm (in 2006) and 3498 mm (in 2010) respectively. During monsoon, the ambient air remains surcharged with moisture.

Lowest minimum and highest maximum temperature observed in the valley during winter and summer is 7.5⁰C (on 16.01.2007) and 40⁰C (on 04.05.2007) respectively, with the average low and high temperature of 9-10⁰C and 37-38⁰C respectively.

Cachar district occupies the geographical area of 3,786 square kilometres (1,462 sq mi) and the second largest district of the state of Assam, India. The Barak is the main river of the district and apart from that there are numerous small rivers which flow from Dima Hasao district, Manipur or Mizoram. The district is mostly made up of plains, but there are a number of hills spread across the district. The climate is Tropical wet with hot and wet summers and cool winters [9].

As per census of 2011 the total population of the valley is 36,12,581 with an average density of population is 543 per sq. Km. According to the 2011 census Cachar district has a population of 17,36,319. This gives it a ranking of 278^th in India out of a total of 640. The district has a population density of 459 inhabitants per square kilometre (1,190/sqmi).

Decadal (2001- 2011) increase of population in the valley is 6,23,784 and the population growth rate of Cachar over the decade 2001-2011 was 20.17%. The district has a sex ratio of 958 females for every 1000 males, and a literacy rate of 80.36%. Population of Barak Valley is far higher than the Population figures of some of the North Eastern states like Nagaland (19,80,602), Arunachal Pradesh (13,82,611), Mizoram (10,91,014), Manipur (27,21,756) and Meghalaya (29,64,007).

DTC/DMCs in accordance with the procedure formulated by RNTCP in the form of Manual for Laboratory Technicians [10].

For diagnosis of tuberculosis, examinations of 3 sputum samples (SPOT-MORNING-SPOT) were performed and the result of morning sample is recorded.

The quality of the sputum sample is ensured first for microscopic examination. A good sample increases the chances of detecting AFB (Acid Fast Bacilli). In physical appearance a good sputum sample appears thick (semi-solid), coughed out deeply from the lungs, purulent (yellowish mucus), sufficient in amount (at least 2 ml). A poor quality sputum sample contains only saliva (watery fluid) or nasal mucus and is small in quantity (less than 2 ml). The slide for examination under microscope is prepared through the following the steps:

First a broomstick (wooden/bamboo) was breakup in to two halves with uneven ends and using the jagged ends of the broken stick, selected and picked up the larger, yellow, purulent portion of the sputum sample from the sample container onto the slide. Separate stick was used for each sample. Then, with another part of the sticks, the sputum was spread evenly to cover 2/3 of the central portion of the slide.

Thereafter, the applicators (broken wooden sticks) are disposed of into a bucket containing disinfectant and the smeared slide was then placed on the drying rack. The size of the smear should be approximately 3x2 cm. The smear should neither be too thick nor too thin. The slides were then allowed for air-drying for 15–30 minutes.

In the next step, the dry slides were fixed and dried by brief heating (at 50-60 ⁰C). After drying of the slides, these were passed over the flame for 3–5 times, for about 3–4 seconds. Heating was done with the smeared side of the slides keeping upwards with the help of forceps and after heating the slides were transferred in the clean slide tray.

Fig-2(a): Number of positive cases of Tuberculosis detected grade wise out of the total number of sputum sample analysed

Fig-2(b): Percentage of positive cases of Tuberculosis of different grades in the area of survey

Out of the total 416 sputum sample of positive cases of Tuberculosis analysed, 96 cases found in “3+” grade of infections (23.07%). Highest percentage (62.50%) of “3+” grade of infections is found in Borkhola DMC followed by DTC at S.M.Dev Civil Hospital, Silchar (30.00%), Dholai DMC (29.80%) and in Udharbond DMC the lowest percentage (10.24%) is found. In Sonai DMC no case of “3+” grade of infection is found out of 38 positive cases investigated [Figure-2(a) & 2(b)].

Out of the total 416 sputum sample of positive cases of Tuberculosis analysed, 99 cases found in “2+” grade of infections (23.79%). Highest percentage (45.19%) of “2+” grade of infections is found in Dholai DMC followed by DTC at S.M.Dev Civil Hospital, Silchar (21.66%), Udharbond DMC (18.07%) and Borkhola DMC (16.66%) and in Sonai DMC the lowest percentage (10.24%) is found. In Sonai DMC only one case of “2+” grade of infection is found out of 38 positive cases investigated [Figure-2(a) & 2(b)].

Out of the total 416 sputum sample of positive cases of Tuberculosis analysed, highest number (137) of cases found in “1+” grade of infections

Housing conditions are used as socio-economic indicators of health and well-being [13, 14, 15, 16]. Poor housing quality and overcrowding are associated with poverty, specific ethnic groups and increased susceptibility to disease [16, 17, 18]. Crowding, poor air quality within homes as a result of inadequate ventilation, and the presence of mold and smoke contribute to poor respiratory health in general and have been implicated in the spread and/or outcome of tuberculosis (TB) [19, 20, 21, 22].

Homes that have inadequate ventilation are often damp or have mold growth resulting from high humidity and condensation. Mold could be considered a proxy indicator of inadequate ventilation; however, homes that have a great deal of air leakage may also have mold [23]. Inadequate ventilation is one of multiple factors that contribute to the development of mold in a home.

Household humidity and encumbered space may also contribute to mold growth in a house. A higher incidence of TB transmission to children has been associated with exposure to environmental tobacco smoke. Children who had contact with index cases who were smokers showed a higher infection rate than those in contact with index cases who were non-smokers [24].

The Mycobacterium tuberculosis bacilli become aerosolized in to droplets of less than 5 μm diameter in an individual having active respiratory TB and the infection of tuberculosis spread with the coughing or sneezing of such individual. An increased density of droplet nuclei in the air leads to an increased risk of infection [21].

The aerosolized droplets settle very slowly and can remain suspended in the air for many hours. Therefore, TB transmission occurs with greater prevalence in poorly ventilated and crowded spaces [15, 21, 25, 26].

In the present study, the population under Borkhola DMC is found to be more susceptible to TB infection. The study revealed highest percentage (62.50%) of “3+” grade of infections in Borkhola DMC followed by 16.66% of “2+” grade of infections and 10.40% infections both in “1+” and “Scanty” grades of infection. On the other hand, the population under Sonai DMC is found to be less susceptible to TB infection in comparison with other DMCs where the study had been carried out.

This difference after adolescence may reflect greater exposure among adult males because of differentiated social roles and economic activities [32], but it also may reflect a genuine sex difference in susceptibility to tuberculosis infection related to a different predisposition to responsiveness to delayed-type hypersensitivity [33].

Accordingly, the more or less middle aged groups i.e. the age group >30-50 years is to be considered most vulnerable for TB infection as highest number of infections of all the four grades is found in this age group. Further, the male subjects are found more susceptible than the females. In the four age groups, segregated here, the males outnumbered the female subjects and highest percentage of afflictions to males occurs in the age group of >50-70 years of age.

Tuberculosis is a multifactorial disorder in which environment interacts with host-related factors, contributing to the overall phenotype. Many factors play a role in individual susceptibility to M. tuberculosis. Understanding the individual balance between degree of exposure and inherited genetic susceptibility to infection, as well as the respective effects of environmental and host-related factors in development of tuberculosis disease, will have strong implications on tuberculosis control and prevention. Finally, the lack of adequate healthcare facilities of the district and inaccessibility of the area creates an alarming situation in terms of M. tuberculosis infections and other types of contagious diseases.

The authors expressed their deep sense of gratitude to the Joint Director of Health Services, Cachar, Silchar, Assam (India) for according necessary/requisite permission to carry out the study in the Govt. Health Centres of the district. The authors are also indebted to the Members of Ethical Committee, Silchar Medical College and Hospital, Silchar, Assam (India) for their approval on continuance of the study with human subjects.

The authors are also thankful to the Technicians of the Govt. Health Centres of Cachar District, Assam for their untiring help and cooperation during the period of study in general and in preparation and examination of smears of sputum samples in particular.