Changes in the bacteriology of acute otitis media associated with the use of the PCV7 vaccine
The pneumococcal conjugate vaccine PCV7 (Prevnar), introduced into clinical practice in the United States in March 2000, has been recommended as a vaccine that effectively prevents the development of infectious diseases. With approval from the American Academy of Pediatrics, the PCV7 vaccine was quickly introduced into the standard US childhood immunization schedule.
Although it is too early to draw conclusions about the effectiveness of vaccination, a number of researchers are already noting significant changes in the structure and antibiotic resistance of pathogens of acute otitis media in older children 7-24 months who received at least 3 doses of PCV7 vaccine.
When comparing the results of a bacteriological study with acute otitis media in the period before the introduction of generalized vaccination (1992-1998) and after (June 2000 - March 2003), a number of differences were noted. Before the introduction of the vaccine, penicillin-resistant pneumococcal strains were homologous to the serotypes contained in PCV7. The good news was a decrease in the overall frequency of Streptococcus pneumoniae from 50% to 35%. The fact that the frequency of isolation of penicillin-resistant strains of S. pneumoniae remained practically unchanged for the researchers was unexpected: 25% before the vaccine was put into practice and 21% after. The isolation of pneumococcal serotypes 6A and 19A not contained in the vaccine increased from less than 10% (pre-vaccination period) to 37%, but the incidence of pneumococcal otitis media caused by strains resistant to penicillin remained unchanged.
It has also been noted that the frequency of isolation of Gram negative microorganisms (mainly untyped strains of Haemophilus influenzae) increased after the introduction of PCV7 from 40% to 65%. The β-lactamase positive (ampicillin resistant) strains of H. influenzae and Moraxella catarrhalis now represent around 50% of the agents responsible for middle ear diseases.
In 2002 and the first half of 2003, 50 children under 30 months of age with acute otitis media who participated in a number of studies evaluating the effectiveness of antibiotic therapy underwent tympanocentesis to isolate the agent pathogen of the middle ear fluid. All children received a full primary cycle of PCV7 vaccine. Similar to the above data, H. influenzae was the first in frequency among the isolated microorganisms (50%), and only 3 strains were resistant to ampicillin. S. pneumoniae was the second most common - 33%, and only 1 in 18 strains isolated had high resistance to penicillin. The third most commonly excreted was Streptococcus pyogenes (10%). In 8% of the samples obtained, there was no etiologically significant flora.
If these data are confirmed by other studies, it will be necessary to recognize significant changes in the hierarchy of pathogens responsible for acute otitis media, which have caused the widespread use of the PCV7 vaccine.