Epidemiologic analysis, limitations

Rickettsia can be stored as freeze-dried powders. In this form, they are easy to disperse. However, because they are living organisms and can be killed during the dispersal process there are limitations to the methods that can be used. They can also be stored and dispersed via infected vectors (e.g., lice, ticks). In most cases, large-scale attacks will be clandestine and only detected through epidemiological analysis of resulting disease patterns. Localized or small-scale attacks may take the form of "anthrax" letters. Even in these cases, without the inclusion of a threat the attack may go unnoticed until the disease appears in exposed individuals (e.g., the initial 2001 anthrax attack at American Media Inc., which claimed the life of Robert Stevens). 

Even if there were no such limitations, epidemiologic analysis is retrospective study it cannot be depended upon for the detection and prevention of potential health hazards to the public. In comparison to epidemiologic studies, animal bioassays are short in duration, relatively inexpensive, easily perfomed under controlled conditions, and are reliable predictors for known human carcinogens. Therefore, from the point of view of identifying and preventing public health hazards, animal bioassay is an invaluable tool. 

There are numerous methods available to identify the potential for chemicals to cause both healtli conditions and adverse effects on tlie eiiviroiiment. These can include, but are not limited to, toxicology, epidemiology, molecular and atomic structural analysis, MSDS sheets, engineering approaches to problem solving, fate of chemicals, and carcinogenic versus non-carcinogenic healtli hazards... 

Epidemiology analyzes statistieal data to deteniiine die relationship between a ehemieal and die exposed populadon. However, positive stadstieal analysis does not always translate into a eause and effeet reladonsliip between the ehemieal and disease in humans. Wlien a eause and effeet reladonsliip between the ehemieal and disease has been established, fiirdier statistieal analysis helps define die upper limit of human toxie risk. 

Epidemiology analyzes statistical data to deiennine tlie lelationslup between a chemical and tlie exposed populatioa However, positive statistical analysis does not always translate into a cause and effect relationsltip between the chemical and disease in humans. Wlien a cause and effect relationsliip between the chemical and disease has been establislied, hirtlier statistical analysis helps define tlie upper limit of hmnan toxic risk. 

Lung Cancer and Mesothelioma Based on an analysis of data from epidemiologic studies of workers who were exposed to asbestos before modem occupational exposure limits were established, EPA (1986) calculated by extrapolation that lifetime exposure to asbestos air concentrations of 0.0001 fiber/mL could result in up to 2 to 4 excess cancer deaths (lung cancer or mesothelioma) per 100,000 people. This air concentration is within reported ranges of ambient air levels (0.00001 to 0.0001 liber/mL). The EPA analysis has been extensively discussed and reviewed in the scientifrc literature (Camus et al. 1998 ... 

Some of the mechanisms and risk factors of methotrexate-associated non-Hodgkin s lymphoma in patients with rheumatoid arthritis have been reviewed, including an analysis of the characteristic features of 25 detailed published cases (122). Although the epidemiological evidence is limited, several reports of spontaneous remission of lymphomas after methotrexate withdrawal strongly support a cause-and-effect relation. 

---