Clinic-based CF Study Links Repeat Hospitalizations to Repeat MRSA Infections

A new study of children with cystic fibrosis found that co-infection with methicillin-resistant bacteria may be associated with increased pulmonary morbidity, especially in children with repeat hospitalizations. The retrospective study, conducted at a U.S. pediatric medical center with high rates of methicillin-resistant respiratory infections, is titled “Clinical characteristics and epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in children with cystic fibrosis from a center with a high MRSA prevalence,” and published in the American Journal of Infection Control.

CF, a genetic disease, is characterized by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) protein that result in regular infective pulmonary exacerbations with opportunistic pathogens, such as Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa).

S. aureus is the most important pathogen of early infection in CF. Methicillin-susceptible S. aureus has been the primary staphylococcal isolate in respiratory cultures from CF patients, but the prevalence of methicillin-resistant strains of S. aureus (MRSA) is increasing. A large observational study found patients with CF and MRSA respiratory infection had worse lung function than patients with methicillin-susceptible strains.

The prevalence of MRSA in CF patients seems to depend on the U.S. geographic region in which these patients live. In 2007, 2008, and again in 2010, the Arkansas Children’s Hospital Cystic Fibrosis Care Center reported the country’s highest MRSA rates. MRSA strains are usually characterized as community-associated (CA) or healthcare-associated (HA), and CA-MRSA has clinical, epidemiologic, and bacterial characteristics distinct from HA-MRSA. HA-MRSA isolates are often resistant to multiple antimicrobial classes, while several of CA-MRSA isolates are resistant only to β-lactams and macrolides.

The research team described the clinical characteristics and molecular epidemiology of MRSA respiratory infection in pediatric CF patients at the Arkansas Children’s Hospital Cystic Fibrosis Care Center in a retrospective review of  medical records from 1997 to 2009.

They found that the prevalence of MRSA increased from 1% in 1997 to 49% in 2009. Fifty-five of the children analyzed, or 26%, had persistent MRSA infection, and 68% of MRSA isolates were hospital-associated (USA 100–SCCmec type II was the most common isolate). Exposure to healthcare facilities and gastrointestinal surgeries was thought to facilitate early acquisition of MRSA. Moreover, 93% of  the HA-MRSA strains were clindamycin resistant. They also found that siblings carried indistinguishable MRSA strains, indicating household MRSA transmission of MRSA, and reported a decrease in mean age of MRSA acquisition over time.

Furthermore, study results showed that children with persistent MRSA had worse pulmonary morbidity, as seen in more frequent hospitalizations and a greater reliance on inhaled medications. Co-infection with methicillin-resistant S. aureus and P. aeruginosa was also associated with increased pulmonary morbidity.

While acknowledging the small sample size and retrospective nature of their study, the researchers concluded that community acquisition of MRSA did not appear to be the main reason for its prevalence at the Arkansas CF center, where most pediatric cases showed hospital-associated MRSA, perhaps as a result of repeat hospitalizations caused by repeat infections. The researchers concluded that the high MRSA prevalence at this care center seems to be multifactorial and in need of further study. Future studies should also focus on methods to prevent MRSA acquisition, both in the hospital and, given transmission rates among siblings, the home environment.