Emergence of a Multiresistant Serotype 19A Pneumococcal Strain Not Included in the 7-Valent Conjugate Vaccine as an Otopathogen in Children

Pichichero ME, Casey JR
JAMA. 2007;298:1772-1778

Summary
The 7-valent pneumococcal conjugate vaccine, introduced in 2000, has been extremely effective in reducing invasive, and to a lesser degree, noninvasive, pneumococcal disease. However, not all strains of pneumococcus are included in the vaccine, and there have long been concerns that nonvaccine strains would become more clinically prevalent.

One previous report on Alaskan children raised the concern that serotype 19A might become problematic, but the isolates in that study were not largely drug-resistant. The authors of the current study have been monitoring middle ear pathogens recovered from their patients, and this report describes their experiences with patients seen from 2003 through 2006, representing 3 respiratory illness seasons.

The study focused on patients with acute otitis media treatment failure (AOMTF) and patients with recurrent AOM. The subjects were 6 months to 36 months old. The authors collected middle ear culture samples by tympanocentesis, and they also collected demographic and clinical information on the subjects. Only children without an anatomic or other reason to be at increased risk for AOM were included.

All subjects had bulging tympanic membranes. AOMTF subjects all had a persistence of symptoms at least 48 hours after beginning antibiotics, and the patients with recurrent AOM had either 3 episodes in 6 months or 4 episodes in 1 year. Of 1816 patients seen during the study period with AOM, 375 (2.1%) met the criteria for either AOMTF or recurrent AOM. Of those children meeting criteria, the authors were able to obtain middle ear fluid from 212. Pathogenic bacteria grew in 162 samples, with 58% of those growing Haemophilus influenzae (nontypable) and 36% growing Streptococcus pneumoniae.

Over the 3 respiratory seasons, there was a decrease in the proportion of S pneumoniae isolates obtained that were covered in the 7-valent vaccine, from 57% to 26% in the final respiratory season. In addition, by the final season, 93% of the nonvaccine strains of S pneumoniae were not susceptible to penicillin.

The authors isolated serotype 19A in 9 total patients, and this organism increased proportionally among nonvaccine serotypes isolated. In these patients, the 19A strain was also multidrug-resistant.

The authors emphasize that of 59 pneumococcal isolates from this study, 15% were 19A strain with significant antibiotic resistance. The authors note that only surgical drainage or use of a fluoroquinolone (not approved for children or for AOM) relieved the symptoms and infection in these 9 patients.

Viewpoint
In the discussion section of the paper, the authors review other studies that have demonstrated the general increase in nonvaccine strains of pneumococcus that are isolated from patients with otitis media. Probably the best take-home message from this is that patients with AOMTF or recurrent AOM really should get drainage for culture to properly identify the causative organism. For some of the study patients, drainage was the only therapy that helped. In any case, knowing the sensitivity profile of the isolates seems more important than ever.