T. Armstrong, ExxonMobil Biomedical Sciences Inc., Annandale, NJ; C. Haas, Drexel University, Philadelphia, PA.
Beginning with the first reports on Legionella pneumophila as the cause of the 1976 Legionnaires’ disease epidemic in Philadelphia, Pa., there has been conjecture about the infectious dose-response in humans. Since then, quantitative microbial risk assessment (QMRA) techniques have evolved and have been applied mainly to water- and foodborne pathogens. Application of QMRA techniques to Legionella may provide insights for setting risk-based limits on air concentration or risk-based limits on the Legionella concentrations in water. The work to extend QMRA to Legionella involved (1) animal model selection and subsequent dose-response modeling using data sets for guinea pigs exposed to aerosols; (2) interspecies extrapolation of the dose-response models to humans using risk assessment techniques, (3) estimation of human exposures for several well-documented outbreaks, (4) estimation of human infection rates for those outbreaks using the QMRA models, and (5) comparison of the estimated risks to the reported infection rates for the outbreaks. The QMRA development demonstrated that the animal model choice is pivotal. The guinea pig data were used in large part, since in vitro data suggested comparable cell-mediated immune responses. The 95% confidence intervals on the QMRA results generally overlapped the respective reported rates of infection, clinical morbidity, or mortality for the three outbreaks evaluated. The few outliers fell within an order of magnitude of the reported rates. The model evaluation results demonstrate the utility of QMRA for understanding the human risk from exposure to virulent stains of Legionella. This may give a basis for setting more rigorous limits on the Legionella concentration in various water aerosol sources, and also for setting standards on air concentrations. This work also suggests that QMRA methods may have utility in improving the understanding of human risks from exposure to other airborne pathogens.
W. Lin, China Medical University, Taichung, Taiwan; J. Pai, F. Wu, Chung Shan Medical University, Taichung, Taiwan.
The characteristics of bioaerosols during the period of routine maintenance of the ventilation system were evaluated in a five-year-old hospital in central Taiwan. A six-stage Andersen viable sampler was used to collect the bacterial and fungal bioaerosols when the workers changed and cleaned the filters of the ventilation system. It was found that the bacterial concentrations could be as high as 2000 CFU/m3, with some ranging from 85 to 183 CFU/m3 before maintenance. In addition, the fungal concentrations would rise dramatically from 700 CFU/m3 to more than 4000 CFU/m3. The six-stage sampler could provide information on bioaerosol size distribution. The results showed that both the geometric mean diameters of bacteria and fungi were changed from 3 µm to 5~6 µm. The analysis of identification of fungal samples showed that the predominant species were Cladosporium spp. before, during, and after the maintenance work.
R. Lee, P. Lam, H. Chen, R. Yung, Centre for Health Protection, Hong Kong; H. Kwok, Hospital Authority, Hong Kong.
Personal protective equipment (PPE) protects health care workers (HCWs) from acquiring infectious diseases at work and reduces opportunities for transmission of microorganisms in healthcare facilities. HCWs need to wear appropriate PPE with gloves, gowns, goggles, and respirators when caring for high-risk patients and carrying out aerosol-generating procedures. Reaerosolization of bioaerosols from contaminated PPE may occur and cause mucosal contacts with microorganisms in these aerosols during removal of PPE. Therefore, a proper sequence in removing contaminated PPE is crucial in preventing infections. A two-factor factorial study was performed with the aid of diluted aqueous fluorescent and the skill of fluorescence photography. The fluorescent was used to visualize self-contamination during removal of PPE and to surrogate bioaerosol exposures. Subjects were asked to put on and remove their PPE, sprayed with diluted fluorescence, in two different sequences (sequence A: glove > gown > cap > face shield > goggles > N95 respirator; sequence B: face shield > goggles > cap > glove and gown > N95 respirator), and two different levels of carelessness (carefully: 2 min, carelessly: 1 min). Fluorescence contaminations on the face glowed under the black light (UVA), and the gross area of exposure was calculated by a computer tool. Data were analyzed with a two-way ANOVA method. The extent of contaminations incurred by sequence A was less than those incurred by sequence B (p<0.001), while it also showed a significant difference between removing PPE carefully and having them removed carelessly (p=0.019). Proper, careful use of sequence A in PPE removal would help minimize self-contamination during removal of PPE compared to sequence B.
H. Perez, Z. Berhane, M. Chilton, Drexel University, Philadelphia, PA; P. Gurian, Drexel University, Philadelphia, PA.
There are several potential respiratory irritants and asthma triggers in most indoor environments. Exposures in the residential environment are of particular concern for children due to the amount of time that they spend indoors at home. This study was conducted to evaluate the relationship between dust endotoxin levels and airborne particulates in the residential environment and activity limitation in asthmatic children. During visits to 63 study participant homes, researchers collected (1) particulate samples with hand-held, six-channel particle counters and (2) dust endotoxin samples from the surfaces on which the asthmatic children slept. Activity limitation in children was measured through the use of the Children’s Health Survey for Asthma, a validated survey instrument of the American Academy of Pediatrics. Statistical analysis indicated a significant relationship between endotoxin levels in dust and activity limitation. However, a significant relationship was not observed between particulate levels and activity limitation. It was concluded that the control of endotoxin levels in the indoor environment may improve quality of life for asthmatic children.
A. Havics, pH2, LLC, Indianapolis, IN.
Since the retraction of a draft quantitative exposure limit originally proposed by the ACGIH Bioaerosol Committee in 1989 for airborne fungal concentrations, many have struggled to find a parallel to the traditional quantitative exposure limit. One approach is to develop control bands that parallel classical risk assessment: hazard identification, dose-response relationship, exposure assessment, risk assessment, and risk management. The hazard identification and dose response (HIDR) can applied to fungal taxa, and the exposure assessment (EA) can be obtained using criteria such as fungal location, fungal severity, population at risk, and expected activity or disturbance. The risk assessment and risk management portions can be then completed by selecting responses based on the ranking of the previous two inputs (HIDR and EA). These can then be compiled in a matrix to present the appropriate responses vs. the estimated exposure risk band. In this way, one can manage the risk in a more uniform manner for efficiency and reduced variability.
S. Viet, Westat, Steamboat Springs, CO; R. Clickner, L. Perez, Westat, Rockville, MD; E. Lehman, NIOSH, Cincinnati, OH.
The prevention of transmission of the human immunodeficiency virus (HIV) and other bloodborne pathogens (BBPs), such as hepatitis B and hepatitis C, in workplace settings has primarily focused on health care workers in hospitals. To develop effective preventive strategies and educational programs, NIOSH determined that further research was needed to define exposures among other occupational groups, in particular correctional health care workers, first responders, and police officers. Formative research for each occupational group included a literature search, assembly of a working group, and conduct of site visits and focus groups. Working groups were comprised of subject matter experts, academicians, and union and trade group representatives with in-depth knowledge of the specific group. Each working group met to discuss development of health communication products. Work site observations of each occupational group were made of (1) procedures for dealing with blood, discarded needles/sharps, etc.; (2) engineering controls to prevent exposures to blood or other potentially infectious body fluids; (3) handling of needles, sharps, body fluids, contaminated materials, etc.; and (4) use and types of personal protective equipment. Relevant written policies and procedures, e.g., the exposure control plan and BBP training materials, were reviewed. Focus groups were also held with representative managers and workers from each group. Based on the formative research, a cost-effective integrated approach was adopted for development of health communication products (posters, brochures, training slides) targeted to the three worker groups. Draft messages and media were tested by semistructured interviews with members of the target audiences. The final products were modified based both on target audience testing results and comments from working group members and CDC reviewers.
M. Parkin, D. Brown, P. Covington, B. Harper, J. Brunner, PPD Inc., Wilmington, NC.
The purpose of this six-year study was to characterize and evaluate the incidence of needlestick injuries prior to and after implementation of needlestick safety devices among Phase I clinical trial research clinics, a setting that has not been evaluated previously. We calculated annual incidence rates as a function of the number of needlestick injuries per 100,000 needle-related procedures performed, representing a true denominator rather than a surrogate, as is commonly reported in the literature. Results indicated that the most frequent sources of injuries were associated with vacuum-tube devices (68%). Other sources included butterfly needles and heparin locks (16%), intravenous (IV) procedures (6%), syringes (3%), and unknown sources (6%). The primary cause of injury resulted from employee error (79%). The remainder were due to a study subject moving (12%), safety device failure (3%), and miscellaneous causes (e.g., improper storage/disposal) (12%). The incidence rate of needlestick injury at baseline was 3.6 (95% confidence interval [CI]: 1.5, 7.5) and 6.6 (95% CI: 3.8, 10.7) during the year of evaluation and implementation, respectively. Needlestick injury rates sharply declined in the four years after implementation, ranging from 1.7 (95 CI: 0.5-4.5) to 2.5 (95 CI: 0.7-6.6), which corresponds to a 32% to 54% decrease from baseline. The Phase I contract research organization setting differs from other health care settings in several ways: (1) “patients” (actually referred to as “study subjects”) are relatively healthy individuals volunteering for clinical research; (2) constant blood draws are required from study subjects; (3) needlestick injuries are the major hazard for research staff in this type of setting; and (4) needle-related procedures are typically timed procedures and thus performed rapidly, with a sense of urgency and often in atypical research circumstances. Consistent with other health care settings and in accordance with OSHA regulations, implementation of a needlestick injury prevention program resulted in decreased rates of needlestick injuries.