In epidemiology, we usually ask three basic questions about a disease in order to get an understanding on its effect on the public health-its public health burden. Incidence is usually reported as the number of cases occurring each year per 100,000 persons in the population. Although the incidence of 1 million whiplash injuries per year is often quoted, this originated with an outdated and incomplete 1971 dataset. More recently, it has been estimated by Croft that as many as 3 million such injuries occur in the U.S. each year. This figure is expected to be the best currently available because it is based on several government databases and accounts for the expected degree of underreporting reported by NHTSA.

This condition is underreported compared to the types of crashes in which people are seriously injured or killed. For example, the National Automotive Sampling System (NASS) is based on the reporting of motor vehicle trauma from EMS, law enforcement, and trauma centers. Since many whiplash victims are not attended by EMS and because many of these injuries are not apparent immediately, they are never reported to the governmental data collection centers. As a result, the incidence figures reported around the world vary widely from a dubious low of 70/100,000 in Quebec, to 700/100,000 in Saskatchewan, and from 417/100,000 in the U.K. to 1172/100,000 in the U.S.

In discussing risk, researchers ask the question: what proportion of the population who is exposed to the putative agent of the disease-in the case of whiplash the agent would be an MVC-actually develop the disease. In very rough terms, in a LOSRIC in the range of 4-10 mph delta V, from an analysis of a fairly large international literature, the risk hovers around 33%. It is higher for rear impact collisions, lower for frontal collisions and intermediate for side impact collisions. Of course, individual risk factors and crash parameters must always be considered. Moreover, the severity of these injuries varies widely, with the more minor not always requiring formal treatment.

The last question concerns prevalence: the proportion of the population that actually suffers from the disease at any given time. Self-limiting diseases can have high incidences and low prevalences. Chronic (incurable) diseases will always have higher prevalence than incidence. For example, during the summer months, the prevalence of the common cold may be low, even though the incidence for the year was high because many people had a cold in the early spring. But every new case of an incurable disease adds to both incidence and prevalence, although the incidence can be low in a disease with high prevalence. (Diabetes, while treatable, is an example of a disease that is incurable.)

In the case of whiplash we attempt to find out how many people who are at risk-which includes just about anyone who travels by car--has chronic neck pain due to whiplash. Our research at the Spine Research Institute of San Diego indicates the number is probably as high as 10%. More interestingly, perhaps, was our finding that as much as 45% of persons with chronic neck pain attribute the pain to a past MVC injury. It is clear that motor vehicle crashes profoundly diminish the nation's health and welfare: a fact that is made all the more poignant by considering the fact that most are potentially preventable.