BOSTON (Reuters) - When someone collapses suddenly, mouth-to-mouth rescue breathing may not be necessary and could lower the chances of survival, researchers said in two studies on Wednesday that found chest compression alone is enough.

The findings add to evidence that the simpler approach works best during cardiopulmonary resuscitation, or CPR.

"Chest compression alone is at least as good, at least as beneficial," Dr. Thomas Rea, medical program director for King County Emergency Medical Services in Washington state and chief author of one of the studies, said in a telephone interview.

The findings come at a time when less emphasis is being placed on mouth-to-mouth rescue breathing, which people often regard as unsanitary anyway, and more emphasis is focusing on properly pressing on the chest at a rate of 100 times a minute — coincidentally, about the same pace as the Bee Gees 1977 disco hit "Stayin' Alive."

"Overall, this study lends further support to the hypothesis that compression-only CPR, which is easier to learn and perform, should be considered the preferred method for CPR performed by bystanders in patients with cardiac arrest," Leif Svensson of the Stockholm Prehospital Center in Sweden and colleagues wrote on the second study. Both studies appeared in the New England Journal of Medicine.

People used to be told to give two breaths for every 15 chest compressions. That formula changed in 2005 to two breaths for every 30 compressions. But animal research has suggested that chest compressions alone may be just as good, perhaps because rescuers continue pumping the victim's heart rather than stopping to give mouth-to-mouth breaths.

In the two studies, researchers worked with emergency telephone operators in Sweden, London and the US state of Washington, who randomly instructed more than 3,000 emergency callers who witnessed a collapse to perform CPR with or without the breathing.

Most of the victims died, but when bystanders did chest compressions alone it slightly increased a patient's chance of leaving the hospital without brain damage; 11.5 percent escaped brain damage if rescue breathing was done while 14.4 percent escaped neurological problems with chest compressions alone, Rea's team found.

In the Swedish test the 30-day survival rate was seven percent with rescue breathing and 8.7 percent without.

The American Heart Association estimates that about 310,000 US adults die annually from sudden cardiac arrest outside the hospital.

The Swedish team stressed that the findings do not apply to cardiac arrest caused by trauma, intoxication or respiratory failure, or to children under the age of eight.

In a commentary in the Journal, Dr. Myron Weisfeldt of Johns Hopkins School of Medicine in Baltimore said CPR courses should continue to teach rescue breathing.

"It is important in cases of cardiac arrest due to obvious respiratory failure, which include most cardiac arrests in children and in some adults," he wrote.

Rea said people with low blood sugar, coma or recovering from a seizure may collapse and appear to need CPR. "We looked at those folks. There was no risk of harm in starting CPR early," he said.