a.
Safety Investigators should use appropriate personal protective equipment (PPE) and practice good personal hygiene when conducting indoor environmental quality, disease outbreaks, and agricultural health investigations that have resulted in medically diagnosed symptoms. PPE may include respiratory protection to prevent inhalation of microbes and microorganismresistant clothing to prevent the transmission (bodily contact with microorganisms) to investigators. Good personal hygiene practices include washing exposed skin and clothing thoroughly and refraining from eating, drinking, or smoking in a contaminated area. These simple steps will help minimize the ingestion, inhalation, or uptake of microorganisms. All samplers, culture plates, equipment, etc. should be handled aseptically to prevent contamination of the samplers and, more importantly, to prevent the spread of potential human pathogens to the worker or the work environment [CDC/NIH 1992; McKinney et al. 1991]. All surfaces, including washed hands, harbor microorganisms or spores unless they are specifically sterilized. Practically speaking, however, not all objects may be sterilized. While disinfection with an oxidizing chemical or alcohol destroys most vegetative cells, these agents do not destroy all spores. Samplers should be disinfected or, if possible, sterilized after each sample collection. Special care should be given to samplers with convoluted inlets or air pathways where microorganisms may accumulate.
b.
Environmental Conditions Temperature and relative humidity (RH) should be recorded over the sampling period. Airborne bacteria will dessicate (i.e., intracellular and extracellular water evaporate) when exposed to unstaurated air. The degree of cellular stress and rate of evaporation increase as relative humidity decreases and temperature increases [Marthi and Lighthart 1990]. In field experiments (greenhouse), survival of certain bacteria was 35- to 65-fold higher at 80% RH than at 40% [Walter et al. 1990]. In laboratory experiments, survival of certain bacteria was virtually complete at low RH but was reduced at RH values above 80% [Cox 1968]. Cox [1987] believes the potential for the movement of the solvent water is an important environmental criterion in assessing survivability of bacteria, viruses, and phages. Limited studies have been made of temperature effects. Temperature induces morphological changes in dimorphic fungi. For example, Histoplasma capsulatum, a pathogen, exists as a spore or mycelial form below 25 oC. However, higher temperatures have been shown to induce a transition from the mycelial form to the yeast form [Salvin 1949]. Like most particles, freshly generated microbial aerosols are nearly always electrostatically charged unless steps are taken to neutralize them. There is very little published information about electric charges on actual workplace aerosols, and even less on bioaerosols [Johnston et al. 1985]. In general, the effect of electrical charge has been overlooked, resulting in the possible bias of sampling results. At RH values above 70% RH, electrostatic phenomena are minimal [Hinds 1982; Cox 1987].
Sampling locations should be selected to assist in evaluation of your hypothesis. If you are evaluating worker exposure, then the samplers should be placed in inhabited areas where worker exposures may be measured. If you are evaluating contamination of a ventilation system, then sampling in the system and at the ventilation louvers would be appropriate. Care 1/15/98
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NIOSH Manual of Analytical Methods
