Time and space uniformity of indoor bacteria concentrations in Chicago area residences

The objective of this article is to assess spatial and temporal variation of indoor gram-positive bacteria and Staphylococcus sp. in 20 urban residences. At each residence, air was sampled at one outdoor site and four indoor sites (rooms) to assess spatial variation and once each season for five consecutive seasons to assess temporal variation. All temporal and spatial comparisons were performed using data obtained by the Andersen sampling technique. A secondary objective of this study is to evaluate relationships among several sampling methods used to measure bacteria levels; since differences in the measured concentrations are expected, the focus is to discern if corresponding measurements relate to each other. Not surprisingly, comparisons among the four sampling systems revealed statistically significant differences, although levels correlated relatively well. Using data only from the Andersen samplers, we conclude that seasonal variation is residence dependent with typically higher summer levels, but a clear pattern of variation could not be established. Room-to-room difference is not statistically significant, but the basement levels render the basement a distinct microenvironment. Indoor concentrations exceeded corresponding outdoor concentrations 75% of the time. Staphylococcus accounts for approximately 27% of the average indoor bacteria levels. The highest levels of gram-positive bacteria are found in the kitchen. The presence of multiple indoor sources with variable emission rates in multiple indoor locations results in bacteria levels that vary with time and space.