Even though a high disease rate is usually taken to be an indication of poor health in a community, a study of Medicare records suggests that this isn't always the case. The high rate may simply be due to better than average diagnosis of a disease: more cases being found.

The researchers base this idea on their finding that death rates for people with one or more serious medical conditions were lower in regions of the country where more of these conditions were diagnosed.

It was when they compared death rates for people with the same number of chronic conditions in different areas of the country that they received a surprise.

If you live in area of the country that has a higher than average rate of heart disease, this may mean that that people there are sicker than average. Or it may reflect the fact that people see more doctors and get more medical tests than and attention than in other parts of the country.

Those who grade doctors' performance and public health officials should be interested in these findings. A low disease rate is generally taken to mean that a good job is being done. This study calls that assumption into question.

The study does not provide clear-cut answers. In fact, it suggests that matters are less clear than they were once thought to be. Sometimes life is like that.

The study looked at nine serious chronic (long-term) medical conditions, ranging from cancer to coronary artery disease, in over five million Medicare beneficiaries in the year 2007. After dividing the country into 306 geographic regions, the researchers looked at the average number of chronic conditions a Medicare recipient was diagnosed with in each geographic region. Since people tend to develop more chronic conditions as they age, many of the study subjects had more than one of these conditions. Nationwide, the average was 0.90, and it ranged from a high of 1.23 to a low of 0.58.

The nine conditions were cancer, chronic obstructive pulmonary disease, coronary artery disease, congestive heart failure, peripheral artery disease, severe liver disease, diabetes with end-organ disease, chronic renal failure, and dementia.

The first thing the researchers noticed was that where you live seems to strongly affect the diagnosis rate. The rates in McAllen, Texas and Miami (1.23) were more than double those in Grand Junction, Colorado and Idaho Falls (0.58). The researchers ascribe this to more doctor visits and tests being conducted per person in the high-diagnosis areas.

They next looked at the relation between mortality and the number of conditions an individual was diagnosed with. The more conditions, the higher the mortality. This isn't unexpected; a person with cancer and coronary artery disease is generally sicker than a person with only one of these conditions.

It was when they compared death rates for people with the same number of chronic conditions in different areas of the country that they received a surprise. A person diagnosed with one of the nine conditions in a high-diagnosis area (Miami) was less likely to die over the course of the study than a person diagnosed with one condition in a low-diagnosis area (Grand Junction). The same was true for individuals diagnosed with two conditions: the higher the average diagnosis rate was in their region, the lower was their chance of death; the lower the average diagnosis rate was in their region, the higher was their chance of death.

The simplest explanation of these results is that in "high-intensity" health care regions, people who have a mild, non-life threatening form of a chronic illness are more likely to be diagnosed with it than in low-intensity health care regions, where diagnosis only occurs when a condition becomes serious.

Only time will tell if this is indeed the correct explanation.

The study results appear in the March 16, 2011 issue of the Journal of the American Medical Association (JAMA).