Multi-resistant Bacterial Strain That Can Cause Ear Infections Emerges; Resistant to Antibiotics

A strain of the bacteria Streptococcus pneumoniae, which can cause ear infections in children, has been detected that is resistant to all FDA-approved antibiotics for treatment of ear infections and is not covered by the pneumococcal 7-valent conjugate vaccine, according to a study in the October 17 issue of JAMA.

Antibiotic resistance to the bacteria pneumococci has been a focus in community-based pediatric medicine because it is the most frequent cause of bacterial respiratory infections, especially acute otitis media (AOM; middle ear infection), which is the most commonly treated bacterial infection in children. The introduction in 2000 of a pneumococcal 7-valent conjugate vaccine (PCV7) in the United States offered considerable promise in curtailing pneumococcal infections in children, with a particularly favorable impact on penicillin- and multidrug-resistant strains, the authors write. In the early years following widespread use of PCV7, the incidence of AOM decreased by 20 percent and the frequency of persistent and recurrent AOM has been reduced by 24 percent, according to background information in the article. Because of overuse of antibiotics for children, there has been concern that a bacterial strain could emerge that would be untreatable by Food and Drug Administration-approved antibiotics.

Michael E. Pichichero, MD, and Janet R. Casey, MD, of the University of Rochester and Legacy Pediatrics, Rochester, New York, examined the shifts in bacteria causing ear infections following the introduction of PCV7 in the strains of Streptococcus pneumoniae that cause AOM, with particular attention to certain pneumococcal serotypes and antibiotic susceptibility. S pneumoniae strains that caused AOM in children receiving PCV7 between September 2003 and June 2006 were identified. All children were from their Rochester, New York, pediatric practice.

Among 1,816 children in whom AOM was diagnosed, tympanocentesis (puncture of the tympanic membrane with a needle to remove fluid from the middle ear) was performed in 212, yielding 59 cases of S pneumoniae infection. The researchers found that one strain of S pneumoniae belonging to serotype 19A was a new genotype and was resistant to all antibiotics approved by the FDA for use in children with AOM. This strain was identified in nine cases (two in 2003-2004, two in 2004-2005, and five in 2005-2006).

Four children infected with this strain had been unsuccessfully treated with two or more antibiotics, including high-dose amoxicillin or amoxicillin-clavulanate and three injections of ceftriaxone; three had recurrent AOM; and for two others, the infection was the first one in their life. The first four cases required tympanostomy (the creation of a hole in the tympanic membrane) tube insertion after additional unsuccessful antibiotic therapies. Levofloxacin was used in the subsequent five cases, with resolution of infection without surgery.

While the studied children represent a relatively small subset of all children in our practice with AOM, these observations are clearly worrisome, especially since there are no new antibiotics in phase 3 clinical trials for AOM in children. The study suggests that an expanded pneumococcal conjugate vaccine to include additional serotypes may be needed sooner than previously thought, with an outer-membrane protein-based vaccine to follow, the authors write.

Changes in the pathogen distribution and antibiotic resistance patterns of bacteria that cause AOM will require continuous monitoring, especially as new vaccines become available.

Reference: JAMA. 2007;298(15):1772-1778.

Source: American Medical Association