That Boston hospital visit this month may be more dangerous than you think. A paper published this week in the Annals of Internal Medicine has supported the longstanding speculation that the “July effect” is real. The “July effect” is the phenomenon of increased hospital patient deaths in July.

The increase in patient deaths is not due to the warm summer weather however. The theory is that more patients die during July because that is when a new class of inexperienced medical school graduates begins residency at teaching hospitals. It is believed that these inexperienced graduates may commit gross medical malpractice mistakes that kill many Boston area patients.

Previous studies failed to consistently support the existence of the “July effect.” One study from the University of Michigan examined over 300,000 patient surgeries over a three year period and failed to note a spike in deaths in July. Another study from the University of Minnesota found no major difference between patient death rates after comparing fall death rates to summer death rates in hospitals.

This new study however systematically reviews data from previous studies and found that deaths at hospitals increase 8 percent in July according to the New York Times. The study acknowledged the inconsistencies in the results of prior research but the data from the best-designed research studies showed an increase in patient deaths. Longer hospital stays also happen in July when more experienced doctors-in-training finish their residency programs and a new batch of graduates begins. “

“This changeover is dramatic, and it affects everything,” the study’s lead author says. “It’s like a football team in a high-stakes game, and in the middle of that final drive you bring out four or five players who never played in the pros before and don’t know the playbook, and the players that remained get changed to positions they never played before, and they never practiced together. That’s what happens in July.”

Source: The New York Times, “Risks: Perhaps July’s Reputation Is Justified,” Roni Caryn Rabin, 7/11/11