Indoor Air and infection (2007)

The Indoor Air community can contribute significantly in dealing with the current concern about a possible influenza pandemic, and control of acute respiratory infectious diseases in general, as revealed by a number of relevant publications in Indoor Air. Recently, the World Health Organization has released new guidelines on infection prevention and control of epidemic- and pandemic-prone acute respiratory diseases in health care (WHO, 2007). In the new guidelines, natural ventilation is considered among the most effective measures to manage infections from serious respiratory disease in health care settings. Such a recommendation for the first time from WHO represents the growing recognition of the association between indoor air/ventilation, and the spread of acute respiratory diseases in buildings. The 2003 severe acute respiratory syndrome (SARS) epidemic showed that viruses in emerging infectious diseases might have jumped from animals (or birds) to human, but it was most probably in buildings that these viruses could spread easily among us. Many studies including those from my own research group (e.g., Li et al., 2005) showed that ventilation and airflow in buildings might have played a significant role in some of the 2003 SARS outbreaks. These findings remind us that the primary purpose of indoor air sciences is for better human health. People spend 90% of their time indoors and people are connected by indoor environments in terms of airborne disease transmission, which is different from exposure to other indoor airborne pollutants. People moves and meets daily from one indoor air environment to another, where the airborne diseases may transmit and thus the infectious pathogens are also ‘transmitted’ from one indoor environment to another in a hospital, a community, a city, and/or between different countries in the world, and thus an epidemic or even a pandemic may occur. To some degree, indoor environments are ‘connected.’ The subtitle for Indoor Air is International Journal of Indoor Environment and Health, implying the multidisciplinary nature of the journal, and the journal community recognizes the importance of indoor for health. In preparing a recent talk for the Roomvent 2007, I found the following two quotes, which may be of a historical interest for studying indoor air and its primary purpose. “The very first canon of nursing, the first and the last thing upon which a nurse's attention must be fixed, the first essential to the patient, without which all the rest you can do for him is as nothing, with which I had almost said you may leave all the rest alone, is this: TO KEEP THE AIR HE BREATHES AS PURE AS THE EXTERNAL AIR, WITHOUT CHILLING HIM” (Nightingale, 1860). “Airborne epidemics are absent from an ecological population provided with adequate air hygiene” (Wells, 1955). The Indoor Air community can contribute to infection control from at least two aspects. The first is in contributing to the continuing search of evidences of proving or disproving a disease can be airborne. The issue of whether some diseases (e.g., for influenza) are transmitted by the airborne route is a highly debatable issue at present. An even more difficult question seems to be what the relative proportion of transmission via airborne route is as compared to large droplet transmission and other routes for a respiratory disease. Such a study may demand us to understand in detail the exhalation flows (Bjorn and Nielsen, 2002) and the respiratory droplets (Morawska, 2006). Airborne evidence of infection disappears rapidly, once the infectious period is over, as the presence of airborne infectious pathogens can disappear from the indoor environment rapidly (by air flow) after the source has been removed. It is difficult to reproduce retrospectively the same indoor air conditions (ventilation and airflow) that existed at the time of the outbreak. Outbreaks are mostly noticed when a significant number of people have been infected, so it is also difficult to estimate, accurately, the exact time of exposure by these people to the infectious pathogens. Thus, the engineering and the medical community have to work together in the most efficient manner using the most updated tools. A multidisciplinary team may be able to accurately and comprehensively measure and document all relevant parameters (relating to both the people and the environment) at the earliest possible time, if it can be rapidly assembled as soon as an airborne infectious disease outbreak is identified. The ventilation modeling and measurement tools, such as computational fluid dynamics and tracer gas techniques can also be useful disease modeling tools. Secondly, we can contribute to develop better engineering control methods of respiratory infectious diseases through a better understanding of different methods, such as building ventilation, the use of filters and UVGI. There are many knowledge gaps here. For example, there was insufficient information/data to specify and/or quantify the minimum ventilation requirements in hospital and non-hospital environments in relation to the spread of airborne infection (Li et al., 2007). A key issue needs to be addressed is how important each individual engineering method is relative to other public health measures, e.g., isolation and quarantine.