According to this article in Newsweek from last July:
the July medical-training period is associated with between 1,500 and 2,750 accelerated deaths every year. In a study of the July phenomenon from which initial findings were released in 2005 by the National Bureau of Economic Research, Harvard Business School health-care economists Robert Huckman and Jason Barro compared mortality rates in teaching and non-teaching hospitals around the country. They found that there are 4 percent more incidences of accelerated death in average-sized teaching hospitals in July and August.
They also found length of stay increased 2%. It is not clear from the above paragraph but the 1,500 to 2,750 deaths is also part of the same study by Huckman and Barro. A good review of the paper is found on this blog, A New Start. Here is a link to the abstract, full article costs $5.
A study done on hospitals in Ohio found no increase in mortality in ICU patients admitted in July through September. It looks like a massive study with rigorous methodology and it is more recent by nearly a decade.
In analyses of over 48,000 patients admitted to ICUs in 5 major teaching hospitals, using a validated method of adjusting for admission severity of illness, several important findings emerge. First, in-hospital mortality and LOS were similar in patients admitted to intensive care units from July through September and during later months of the academic year. Moreover, results were consistent when July, August, and September were analyzed separately, and there was no discernible pattern of variation when examining outcomes for individual months over the entire year. Furthermore, we were unable to detect differences when individual academic years, surgical and nonsurgical patients, and individual hospitals and ICUs were examined separately. These results were all similar in analyses of roughly 108,000 patients admitted to minor teaching and nonteaching hospitals.
With its unremarkable findings and disruption of the common wisdom is it any wonder that it is given short shift in the Newsweek article.