A tough, virulent strain of methicillin-resistant Staphylococcus aureus is five times more deadly than other MRSA strains, and typically affects older patients, according to new findings.

While most strains of MRSA hit adults with an average age of 52, this strain, called USA600, tends to infect those around 64 years old, say researchers at the Henry Ford Hospital’s division of infectious diseases. At least partially resistant to common antibiotic treatments, USA600 infects the bloodstream. In a study of patients infected with the strain, roughly half died within one month of developing the infection, according to their report, which was presented last weekend at the annual gathering of the Infectious Diseases Society of America.

Other studies presented at the IDSA conference found that antibiotic-resistant bacteria continues to be a major health concern as resistance grows and new treatments become harder to find. C. Difficile, usually found in nursing homes and healthcare settings, has begun infecting those who have never been to the hospital, according to one report. Another study found a 211% increase in the rate of MRSA infection in emergency rooms between 2000 and 2008.