A new analysis about the chances of being injured or harmed during treatment in Canadian hospitals finds that some errors occur with disturbing frequency.

According to the report by the Canadian Institute for Health Information (CIHI), the chances of patients receiving the wrong medication or wrong dose was about 1 in 10 in 2005.

The chances of an adult contracting an infection while in an acute care hospital are about the same: 1 in 10, while the chances of a child contracting an infection while in hospital are about 1 in 12.

Incidents in which a foreign object is left behind in a surgical cavity are less common, affecting about 1 in 3,000 patients in Canadian hospitals (outside of Quebec and parts of Manitoba). Yet that still adds up to more than 200 incidents per year between 2003-2004 and 2005-2006.

Previous studies show that obese patients are at higher risk of having a foreign object left behind after surgery, though the reasons aren't clear.

Other higher risk groups include: patients who undergo emergency operations, those who have an unexpected change in operation or those who have a change in nursing or surgical staff during a procedure.

"The consequences of leaving a sponge or other foreign object in after surgery can be significant, but experts suggest that targeted strategies can reduce the risk," says Dr. Indra Pulcins, CIHI's director of Health Reports and Analysis.

Those strategies include following a practice of sponge and instrument counts, as well as vigilant inspection of body cavities when the surgery is complete.

One of 21 mothers giving birth by vaginal delivery in hospital experience obstetrical traumas, such as lacerations of the cervix, vaginal wall, or injury to the bladder or urethra. Between April 2003 and March 2006, there were more than 9,100 reported obstetric traumas in Canadian hospitals, outside of Quebec each year.

One in 141 babies born in hospitals outside of Quebec experienced birth trauma, such as injuries to the scalp, skull fractures, or injuries to nervous systems. This represents more than 1,700 cases yearly.

Previous research suggests that risk factors for trauma during birth include newborns weighing more than 4 kg, long labour, the need to use instruments during delivery and a woman's position during birth.

CIHI's analysis found that 3.6 out of every 1,000 patients in Canadian hospitals (outside Quebec and parts of Manitoba) experience a pulmonary embolism while in hospital. An embolism occurs when a blood clot or globule of tissue travels through the veins and into the lung, and can occur when patients are bed-ridden or sedentary for long periods.

Dr. Jennifer Zelmer, CIHI's vice-president of Research and Analysis says tracking medical errors and adverse incidents is important in learning how to prevent them.

"While we do not know how to prevent all adverse events, tracking how often they occur and understanding the factors that contribute to them is an important step in improving patient safety," says Zelmer.

Experts have suggested a number of strategies to reduce the risk or errors and patient harm, including automated drug alerts and medication reconciliation -- the process designed to prevent medication errors at patient transition points.