Many of the pediatric deaths and critical illnesses in the 2009-2010 H1N1 influenza pandemic occurred among children who acquired antibiotic-resistant bacterial infections in addition to being infected with that flu virus, a study in the journal Pediatrics reports Monday morning.

The study looked at 838 cases in which children (under age 21) infected with H1N1 were admitted to 35 pediatric intensive care units (PICUs) across the country. The median age of children who were critically ill with an H1N1 infection was six. Simultaneous infection with methicillin-resistant Staphylococcus aureus (MRSA) bacteria in the lungs increased eightfold the risk that children with no pre-existing conditions would die, the study found. Here’s the frightening part: Most of the children were treated with an antibiotic (vancomycin) aimed at combating those bacteria — but to little apparent benefit.

Of the children whose records the study examined, 8.9 percent died. Sixty-two percent were critically ill from H1N1 infection without there being evidence of bacterial infection when they were admitted to the PICU. Vaccination status was unknown for most of the children, largely because the H1N1 vaccine wasn’t made ready until the pandemic was well underway. Many severe illnesses and deaths occurred among young people with previously existing, chronic neurological and immune-system conditions.

More than 88 percent of the children received the antiviral medication oseltamivir (Tamiflu), but only about 6 percent of them started such therapy before being admitted to the PICU. The authors speculate that earlier antiviral treatment could perhaps prove effective in reducing pediatric mortality associated with the H1N1 virus.

The study notes that protocols for identifying MRSA infections in children early on aren’t well established and that remedying the protocols might help curb deaths from H1N1, a strain of influenza that the authors note continues to circulate throughout the world.

The study, led by Children’s Hospital Boston, is the largest nationwide investigation of influenza in critically ill children to date, according to its authors.

According to a recent report from the U.S. Centers for Disease Control and Prevention, about a quarter of the pediatric deaths in the most recent flu season (2010-2011) were among children infected with the H1N1 strain.