Study sensitivity: Evaluating the ability to detect effects in systematic reviews of chemical exposures.

A critical step in systematic reviews of potential health hazards is the structured evaluation of the strengths and weaknesses of the included studies; risk of bias is a term often used to represent this process, specifically with respect to the evaluation of systematic errors that can lead to inaccurate (biased) results (i.e. focusing on internal validity). Systematic review methods developed in the clinical medicine arena have been adapted for use in evaluating environmental health hazards; this expansion raises questions about the scope of risk of bias tools and the extent to which they capture the elements that can affect the interpretation of results from environmental and occupational epidemiology studies and in vivo animal toxicology studies, (the studies typically available for assessment of risk of chemicals). One such element, described here as "sensitivity", is a measure of the ability of a study to detect a true effect or hazard. This concept is similar to the concept of the sensitivity of an assay; an insensitive study may fail to show a difference that truly exists, leading to a false conclusion of no effect. Factors relating to study sensitivity should be evaluated in a systematic manner with the same rigor as the evaluation of other elements within a risk of bias framework. We discuss the importance of this component for the interpretation of individual studies, examine approaches proposed or in use to address it, and describe how it relates to other evaluation components. The evaluation domains contained within a risk of bias tool can include, or can be modified to include, some features relating to study sensitivity; the explicit inclusion of these sensitivity criteria with the same rigor and at the same stage of study evaluation as other bias-related criteria can improve the evaluation process. In some cases, these and other features may be better addressed through a separate sensitivity domain. The combined evaluation of risk of bias and sensitivity can be used to identify the most informative studies, to evaluate the confidence of the findings from individual studies and to identify those study elements that may help to explain heterogeneity across the body of literature.

How credible are the study results? Evaluating and applying internal validity tools to literature-based assessments of environmental health hazards.

Environmental health hazard assessments are routinely relied upon for public health decision-making. The evidence base used in these assessments is typically developed from a collection of diverse sources of information of varying quality. It is critical that literature-based evaluations consider the credibility of individual studies used to reach conclusions through consistent, transparent and accepted methods. Systematic review procedures address study credibility by assessing internal validity or "risk of bias" - the assessment of whether the design and conduct of a study compromised the credibility of the link between exposure/intervention and outcome. This paper describes the commonalities and differences in risk-of-bias methods developed or used by five groups that conduct or provide methodological input for performing environmental health hazard assessments: the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) Working Group, the Navigation Guide, the National Toxicology Program's (NTP) Office of Health Assessment and Translation (OHAT) and Office of the Report on Carcinogens (ORoC), and the Integrated Risk Information System of the U.S. Environmental Protection Agency (EPA-IRIS). Each of these groups have been developing and applying rigorous assessment methods for integrating across a heterogeneous collection of human and animal studies to inform conclusions on potential environmental health hazards. There is substantial consistency across the groups in the consideration of risk-of-bias issues or "domains" for assessing observational human studies. There is a similar overlap in terms of domains addressed for animal studies; however, the groups differ in the relative emphasis placed on different aspects of risk of bias. Future directions for the continued harmonization and improvement of these methods are also discussed.

The national study to prevent blood exposure in paramedics: rates of exposure to blood.

OBJECTIVE: The purpose of this analysis is to present incidence rates of exposure to blood among paramedics in the United States by selected variables and to compare all percutaneous exposure rates among different types of healthcare workers. METHODS: A survey on blood exposure was mailed in 2002-2003 to a national sample of paramedics. Results for California paramedics were analyzed with the national sample and also separately. RESULTS: The incidence rate for needlestick/lancet injuries was 100/1,000 employee-years [95% confidence interval (CI), 40-159] among the national sample and 26/1,000 employee-years (95% CI, 15-38) for the California sample. The highest exposure rate was for non-intact skin, 230/1,000 employee-years (95% CI, 130-329). The rate for all exposures was 465/1,000 employee-years (95% CI, 293-637). California needlestick/lancet rates, but not national, were substantially lower than rates in earlier studies of paramedics. Rates for all percutaneous injuries among paramedics were similar to the mid to high range of rates reported for most hospital-based healthcare workers. CONCLUSIONS: Paramedics in the United States are experiencing percutaneous injury rates at least as high as, and possibly substantially higher than, most hospital-based healthcare workers, as well as substantially higher rates of exposure to blood on non-intact skin.

Provision and use of personal protective equipment and safety devices in the National Study to Prevent Blood Exposure in Paramedics.

BACKGROUND: Paramedics are at risk for human immunodeficiency virus, hepatitis B virus, and hepatitis C virus infection from occupational blood exposure. This study examined how often paramedics are provided with personal protective equipment (PPE), sharps containers, and selected safety devices by their employers; the frequency with which paramedics use sharps containers and these safety devices; and paramedics' attitudes regarding this equipment. METHODS: We conducted a mail survey among a nationally representative sample of certified paramedics. California was oversampled to allow for separate estimation of proportions for this population. RESULTS: The final sample included 2588 paramedics, 720 of whom were from California (adjusted response rate, 55%). Paramedics in California were provided safety devices more often than paramedics in the United States as a whole. For each type of device, there was at least a 40% increase in use when the device was always provided compared with when it was not always provided. Eighty-four percent of paramedics thought that safety needles significantly reduce blood exposure, but substantial percentages thought that safety needles, eye protection, and masks interfere with some medical procedures. Approximately one fifth said that they need more training in the use of safety devices and PPE. CONCLUSION: Lack of access to safety devices is the major barrier to their use, and the higher rates of provision and use in California may be the result of the state's early safety needle legislation. Increased provision, training, and improvement of safety equipment are needed to better protect paramedics from blood exposure.

Blood exposure among paramedics: incidence rates from the national study to prevent blood exposure in paramedics.

PURPOSE: The aim of the study is to estimate incidence rates of occupational blood exposure by route of exposure (needlesticks; cuts from sharp objects; mucous membrane exposures to the eyes, nose, or mouth; bites; and blood contact with nonintact skin) in US and California paramedics. METHODS: A mail survey was conducted in a national probability sample of certified paramedics. RESULTS: Proportions of paramedics who reported an exposure in the previous year were 21.6% (95% confidence interval [CI], 17.8-25.3) for the national sample and 14.8% (95% CI, 12.2-17.4) for California. The overall incidence rate was 6.0/10,000 calls (95% CI, 3.9-8.1). These rates represent more than 49,000 total exposures and more than 10,000 needlesticks per year among paramedics in the United States. Rates for mucocutaneous exposures and needlesticks were similar (approximately 1.2/10,000 calls). Rates for California were one third to one half the national rates. Sensitivity analysis showed that potential response bias would have little impact on the policy and intervention implications of the findings. CONCLUSION: Paramedics continue to be at substantial risk for blood exposure. More attention should be given to reducing mucocutaneous exposures. The impact of legislation on reducing exposures and the importance of nonintact skin exposures need to be better understood.