infectious disease

Airborne transmissions take place as a transport of virus or bacteria via the aerosol flow in rooms. The distribution of aerosols tends to be evenly distributed if the flow in the room is fully mixed. The aerosols distribution will be different if the room air is stratified. A vertical temperature distribution may create stratified layers with either lower or higher concentrations of exhalation from the infected person.

In response to the COVID-19 pandemic, many organizations have recommended improved ventilation to reduce the risk of indoor airborne infectious disease transmission. These recommendations include increasing outdoor air rates and filtration efficiencies, as well as verifying that ventilation systems are operating as intended. There have also been many recommendations to monitor indoor CO2 concentrations as indicators of ventilation or infection risk, in some cases with quantitative concentration limits.

The indoor environment can play a significant role in the transmission and exposure of various contaminants. In some emerging aerial infections, such as influenza virus, tuberculosis virus, and other biological and chemical contaminants, the airborne route of transmission is thought to be important to evaluate exposure health risk.

The ventilation system of a community hospital deteriorated progressively over a period of years until it no longer met regulatory guidelines. The publicly funded military facility hospital asked for funding for repairs but they were not available. The funding request was met when an increase in infections was identified and high-risk operations had to be curtailed. The problems were solved entirely when the new ventilation system was in place.

This was a study of the possible causes of an outbreak of encephalitis on Saipan in October 1990. The virus was not isolated but patients seroconverted to Japanese encephalitis (JE) virus, suggesting the first known outbreak of the disease on American territory since 1947. Ten cases were found in a population of 40,000. In a survey after the outbreak, the prevalence of antibody to JE virus was 4.2% among 234 native Saipan residents. Risk factors for infection were age, crowded living conditions and lack of air conditioning.

This study investigates the effects of ventilation on the spread of airborne diseases. After four weeks contact with a colleague suffering from cavitary tuberculosis 27 of 67 office workers had documented tuberculin skin test conversions. Complaints by workers for more than two years previously prompted studies of the air quality in the building before and after the tuberculosis exposure. Concentrations of Carbon Dioxide in many parts of the building exceeded recommended levels, indicating inadequate ventilation with external air.

Describes a case of primary and secondary infections of TB in an office environment in Tokyo, Japan. It was found that the ventilation system was frequently closed down to save energy, resulting in high CO2 concentrations. Concludes that the secondary infections were due to insufficient ventilation.

An investigation of the source of an MRSA outbreak at a UK hospital found that the cause was an intermittently operated ventilation system. Ventilation grilles were found to be contaminated with EMRSA-15. It was found that daily system shutdown was causing a temporary negative pressure which drew air in from the ward and likely contaminated the outlet grilles. The index for the outbreak was a patient moved into the hospital from another large hospital. States that it is likely that contaminated air was blown back from the grilles at switch-on.

A newly built nursing home was analysed to establish why there had been a significantly lower attack rate in this building during a type A influenza epidemic. Measurements were taken of the number of respiratory illnesses and influenza cultures in consenting symptomatic residents, and of building characteristics. Of the four buildings in the home, Building A had significantly fewer culture-confirmed cases than the other buildings. Building A's ventilation system was unique, it had more public space per resident, and did not have office space serving the whole complex.

Due to infection risks, high demands are set for the air quality in operating theatres. This is normally realised through the use of a downflow plenum. In this article the application of a fluid flow simulation program (CFD), as a design tool for the evaluation of a new ventilation design for operating theatres, is discussed. In this case an alternative downflow plenum has been investigated, that differs from the currently common designs. The use of CFD allowed for the examination of important design criteria and the resulting adjustments to the design.