Poor ventilation

Ventilation is an important determinant of airborne infections. Poor ventilation at a patient's residence or at a healthcare facility, will result in more risk attached for any airborne infections.

Poor Ventilation and Inadequate Air Circulation as Risk Factors for Tuberculosis (TB)

• The tiny TB bacilli, Mycobacterium tuberculosis, which is 1-5 microns in diameter, floats through the air when people who have active tuberculosis cough, sneeze, talk or sing, and spreads to other people when they breathe in the air containing the floating droplet nuclei.
• The lighter TB bacteria can linger in the air for long periods, worsening the accumulation with every cough or sneeze, when there is poor ventilation and inadequate air circulation.
• The amount of circulating air and how much and how fast it circulates, are vital elements of transmission:
  • In ambient, static air, infectious droplet nuclei containing one or more tubercle bacilli remain buoyant in the air for a prolonged period of time, for up to 6 hours.
  • But in spacious spaces or places where the air moves around faster (e.g. with the use of fans, cross-ventilation with windows) the TB bacilli is quickly dispersed
• Thus, there are 3 important points to be noted:
  • The longer a person is around a contagious adult in areas with poor ventilation and insufficient air circulation, the more likely that person will become infected
  • Poor ventilation also worsens the accumulation, thereby increasing the chances of transmission by the sheer number of bacteria in the air
  • People can get infected even if the infected person is not in the room, because the bacilli has not been fully dispersed in a poorly ventilated room

On the other hand, adequate ventilation can reduce the risk of infection through dilution and removal of TB bacilli. When clean or fresh air enters a room, by either natural or mechanical ventilation, it dilutes the concentration of airborne particles, such as droplet nuclei, in the room air. Dilution reduces the likelihood that a person in the room will breathe air that may contain infectious droplet nuclei. Ensuring adequate ventilation includes the use of:

1. Natural methods to ensure unrestricted flow of air via open doors and windows, and preventing obstruction of doors and windows
2. Mechanical methods such as using ceiling fans in homes, exhaust fans in TB labs, use of negative air pressure/HEPA filters in hospital settings

Image: Showing importance of adequate ventilation; Source: Pollution Control, Government of India

Resources

• Tuberculosis Infection Control; Curry TB Centre; 2011
• Guidelines on Airborne Infection Control in Healthcare and Other Settings; Directorate General of Health Services Ministry of Health & Family Welfare, 2010
• WHO - Tuberculosis

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