Why do we live so long when our ancestors only a few generations ago did not? Is our longevity attributable to the spectacular advances in curative medicine such as penicillin, critical care units and cardiac bypass surgery, or is it the result of innovations in public health--sanitation, refrigeration and clean water? This debate ebbs and flows among physicians and health policy makers, with most weighing in on the side of public health. The dramatic statistical improvements in our health over the past century have come because our water is pure, we are immunized against many infectious diseases and the food we eat is free of microbial contamination.

The expectation of protection, in fact, is deeply inculcated in us. Without much reflection, we count on freedom from epidemics, new and mysterious diseases, and death at the hands of unknown bacterial killers. We travel, we eat and we breathe with relative confidence that some agency of the public good has certified these activities as healthy.

When things go awry, however, when an illness of unknown cause appears, the effect is doubly devastating. Not only are we prey to the disease and appropriately worried about it, but we suddenly call into question the shield of vigilance that has been guarding us. Is it adequate? How has it been penetrated? Is a plot afoot rather than some malevolent but natural twist of biology? How will it be stopped?

Such was the spasm of medical attention and media concern that greeted the outbreak of a flu-like pneumonia following an American Legion convention in Philadelphia in the summer of 1976. One hundred twenty-eight convention participants contracted the mystery ailment dubbed Legionnaires' disease. Of those, 27 died--disturbing figures but trifling compared to other causes (auto accidents, for example) of illness and disease occurring in the population in general. What captured the attention of America was the element of the unknown and the concomitant ripple of fear it sent through the nation.

Gordon Thomas and Max Morgan-Witts have recorded that apprehension and drama in "Anatomy of an Epidemic," a lengthy, personalized documentary of the episode. The writers are veterans of journalistic narrative, having collaborated previously on books on Guernica, the bombing of Hiroshima and the stock-market crash. They bring their encyclopedic techniques and their considerable reportorial abilities to bear on a vast quantity of information surrounding the convention and its aftermath. They skillfully weave the historic events of the summer of 1976--the Bicentennial, the national political conventions, the growing debate about swine flu, the tenuous condition of the Bellevue-Stratford Hotel--into a backdrop for the story. The account moves smoothly and entertainingly from the home towns of legionnaires to the inner sanctums of the Center for Disease Control (CDC) in Atlanta, from the kitchens of the Bellevue-Stratford to the offices of the state health commissioner in Harrisburg. The actors--victims and epidemiologists, hotel employes and politicians--are developed dramatically and colorfully.

The book has its problems, though. It is simply too long. The reader must contend with explicit and lengthy descriptions of a cardiac resuscitation, an autopsy, a trip through the air-conditioning ducts in the Bellevue-Stratford, and more. At times it seems that the text is driven by a well-planned but poorly concealed formula that calls for a little sex here (a hooker in action) and a high-speed ride in a police car there. A sparer and more precise use of the masses of data and anecdote assembled by the authors would have served their story well.

Additionally, Thomas and Morgan-Witts struggle with an inevitable problem of writing contemporary history. Without the prism of time, it is very hard to judge who are the true heroes and who are the goats. While it quickly became clear that Legionnaires' disease didn't spread from its victims to others, relieving much of the anxiety surrounding it, its cause was not immediately determined. This led to continued speculation of all sorts (political terrorists, Army biological warfare, outer space) and congressional hearings that heaped abuse on the CDC for failing to pin down the agent. After six months of painstaking lab work the CDC did, in fact, isolate the bacteria and demonstrate a firm epidemiological relationship to the convention. The authors handle the problem of judgment by treating everybody gently. There are heroes--particularly the medical investigators--but no goats, a fair solution but a bland one.

"Anatomy of an Epidemic" performs an important function. It details the impressive and little-publicized network of physicians, epidemiologists and lab scientists that forms a public fail-safe against the mutations and permutations of our microbiological enviromnent. This system is sometimes forgotten amidst our enthusiasm for elegant new technologies--surgical lasers and CAT scanners--but it remains the bedrock of our health, public and, ultimately, personal. Thomas and Morgan-Witts have done well to document it in action.