Spike in Disease Doesn't Always Mean an Epidemic

Many scientists believe that what happened in Livermore with skin cancer is happening with other illnesses.

Earlier Detection

Between 1987 and 1992, the incidence of prostate cancer jumped 85 percent. Why? Because something dramatic happened in 1987: Doctors started to perform a simple blood test to screen for prostate specific antigen, or PSA, levels, a marker for prostate cancer.

Almost overnight, more early-stage cases were detected and treated. What looked like an epidemic of prostate cancer was, in fact, major progress. Before that time, cases were detected only if a man received a transurethral resection of the prostate, or TURP; the procedure involved inserting a small telescope into the prostate through the penis and chipping away pieces of the prostate for analysis. Not surprisingly, doctors performed the procedure only when truly necessary.

Then, between 1992 and 1996, rates of prostate cancer dropped almost as steeply as they had risen.

"This didn't mean there was necessarily more disease during the rise or less disease during the decline," says Thomas M. Pisansky, a professor of oncology at the Mayo Clinic College of Medicine. "Most researchers agree that the rise was due to the PSA, and the fall was due to getting all those men diagnosed."

It's as if a fisherman suddenly found a better way to catch fish. At first, he'd have a high yield, but over time there would be fewer fish to catch.

Lowering the threshold for diagnosis can quickly change the prevalence of a disease. Take hypertension (high blood pressure), a condition that affects more than 50 million Americans. Hypertension awareness campaigns since the 1960s have lowered mortality from coronary heart disease and stroke. But the prevalence of hypertension has risen over the past 10 years.

Fast food and a more sedentary lifestyle likely have played a part, but so has a redefinition of the disease.

In 2003, an expert committee concluded that individuals with a diastolic pressure (the bottom number in a blood pressure reading) of 80 to 89 (then on the high end of "normal") were at risk of developing hypertension-related disease and should be called "prehypertensive."

Physicians soon began to treat such patients for hypertension, and, for insurance and medical records, they were coded in the same way as someone with a much higher blood pressure. The number of diagnosed cases of hypertension thus rose.

The average patient with what was newly considered "high blood pressure" also fared better because the pool of patients with hypertension now included some previously "normal" people. This might also help explain part of the drop in mortality among people with hypertension: The average patient with the diagnosis was now healthier.

Thresholds have dropped for other common diseases, including obesity and diabetes, and the criteria for disease classifications have broadened. Autism, for example, once a narrowly defined disorder, is now used to describe a wide spectrum of severity, from the profoundly mentally retarded person to the socially awkward mathematics professor.