Shobha Shukla, CNS ColumnistSeveral interesting aspects about the survival of the tuberculosis (TB) causing aerobic bacteria in real life environments were discussed in a lively talk by Dr Tushar Sahasrabudhe of Dr DY Patil Medical College, Pune, on the last day of the 20th National Conference on Environmental Sciences and Pulmonary Diseases (20th NESCON), organized by the Academy of Respiratory Medicine under the auspices of Environmental Medical Association in Mumbai.
He not only addressed issues like contribution of public spitting in the spread of TB; spread of TB infection in hospital wards, but also busted several myths surrounding the dreaded disease.
We seem to have become inured to the coughing and spitting by people on the road or in our vicinity. Many doctors, including chest physicians, believe that while droplets floating in the air can spread TB, those on the road (like of spit) cannot infect us. But according to Dr Sahasrabudhe contaminated cough sputum on the road can infect us just like the sputum of a TB patient (who is not on anti-TB therapy and is still sputum smear positive) in the home or hospital setting.
There are many myths about the infectious TB bacteria. There is a general belief in society (and even among doctors) that as the roadside spit dries up in a few minutes and does not get aerosolized to inhalable sized particle (less than 5 micron), it is non- infectious. However, a single cough or sneeze produces 5000 droplets while a sputum producing cough bout generates more than 20,000 droplets. Some of these particles, which travel far and wide, are less than 5 microns in size and hence inhalable. Similarly, once the spit on the road dries, sweeping and dusting aerosolizes it, producing at least few particles which are less than 5micron in size. If they are contaminated with TB bacteria, they reach the lungs of persons who inhale them causing a latent TB infection (not active TB disease).
It also believed that that ultraviolet rays in sunlight kill TB bacteria in a very short period and so does tobacco. But truth is stranger than fiction.
Dr Sahasrabudhe and his team carried out a study to evaluate the duration of viability of TB bacteria in sputum of pulmonary TB cases under various environmental conditions.
Sputum samples of 67 sputum positive pulmonary TB cases were taken and each sample was divided into 4 parts: A, B, C and D.
Samples A were sent for 'culture' testing on day zero. Samples B were stored in dark and portions sent for 'culture testing' on days 1, 2, 3, and 7. Samples C were exposed to direct sunlight from 9am-4pm and portions sent for culture testing on days 1, 2, 3 and 7. Samples D were mixed with tobacco spit (with well- defined tobacco concentration to match real life situations). Half of them were kept in dark and the rest in sunlight. Portions were sent for culture on days 1, 2, 3 and 7.
The results of the 13 cultures done for each of the 67 cases under examination were an eye opener indeed. Out of the 67 cases, only 50 eventually grew TB bacteria in culture. 37 of these 50 cases were new cases and 13 were retreatment (out of which 2 turned out to be MDR-TB cases). For samples exposed to direct sunlight, the bacteria were still alive after 24 hours in 76% cases, after 48 hours in 34% cases and after 3 days in 4% cases. In 52% of the tobacco mixed samples kept in dark TB bacteria were alive even after 7 days.
Although more research needs to be done, yet this study does raise important questions: TB bacteria perhaps survives much longer in direct sunlight (longer than the widely believed theory that sunlight kills TB bacteria in 15-20 minutes exposure), and that tobacco spit does not kill TB bacteria.
Another study was conducted by Dr Sahasrabudhe and his team on 58 non-TB patients admitted in a hospital and 98 visitors. After a mean period of 6.3 days, 17% of the patients and 6.56% visitors tested positive for latent TB infection which may or may not reactivate. Yet chances for reactivation remain even after 20 years just because they visited someone in the hospital ward.
Incidence of TB infection after 1 year of joining college was as high as 23% in medical students (as opposed to 6% in engineering students) according to a study conducted in Brazil.
Another study done in Thailand found that incidence of TB in healthcare workers in a TB ward was 72% while in those working in other wards was 63%. So working in TB wards did not significantly increase the risk of acquiring TB. Among tuberculin reactors development of TB is not influenced by re-exposure to infection and among heavily exposed subjects tuberculin reactors enjoy distinct protection.
There is a need to contain the transmission of TB bacteria and prevent/control its spread. Providing high quality TB testing and standard treatment must go hand in hand with following basic hygiene in hospitals and in our daily lives. The minimum infection control measures that can be taken in hospital settings are: separate TB wards with good cross ventilation and UV tube lights; twice daily wet mopping of floor; good protocols of sputum collection and disposal; use of face masks by TB patients and use of personal protective devices by healthcare workers.
Public coughing and spitting also contribute to the spread of TB
So coughing etiquette must be inculcated in all of us to minimize spread of cough droplets in air. One must cover the mouth and nose with a tissue/hanky while coughing or sneezing which should be disposed off and hands washed thoroughly. If there is no tissue one can cough or sneeze into the upper sleeve or elbow but not in the hands. Public spitting needs to be strongly curtailed. Practicing good hygiene will go a long way in controlling the spread of not only TB but other air/water borne diseases as well.
Shobha Shukla, Citizen News Service (CNS)
3 July 2014(The author is the Managing Editor of Citizen News Service - CNS. She is a J2J Fellow of National Press Foundation (NPF) USA and received her editing training in Singapore. She has earlier worked with State Planning Institute, UP and taught physics at India's prestigious Loreto Convent. She also co-authored and edited publications on gender justice, childhood TB, childhood pneumonia, Hepatitis C Virus and HIV, and MDR-TB. Email: shobha@citizen-news.org, website: www.citizen-news.org)
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