Abstract
The aim of this study was to determine the serotype and clonal distribution of pneumococci causing acute otitis media (AOM) and their relationship with recurrences and mixed infections with other microorganisms under the influence of the 7-valent pneumococcal conjugate vaccine (PCV7). To do this, all pneumococcal isolates collected from the spontaneous middle-ear drainage of children <5 years old diagnosed of AOM by their pediatrician or their general practitioner from 1999 to 2010 were phenotypically characterized and the most frequent serotypes were genotyped. In the 12-year study, 818 episodes of pneumococcal AOM were detected, mostly (70.5%) in children younger than 2 years old. In 262 episodes (32%), the pneumococci were isolated with another bacterium, mainly (n = 214) Haemophilus influenzae. Mixed infections were similar in children under or over 2 years old. The most frequent serotypes were 19A (n = 227, 27.8%), 3 (n = 92, 11.2%) and 19F (n = 74, 9%). Serotypes included in the PCV7 sharply decreased from 62.4% in the pre-vaccination (1999–2001) to 2.2% in the late post-vaccination period (2008–2010). Serotype diversity steadily increased after the introduction of the PCV7 but decreased from 2008–2010 due to the predominant role of serotype 19A isolates, mostly ST276 and ST320. The prevalence of serotype 3 doubled from 6.1% (20/326) in 1999–2004 to 14.6% (72/492) in 2005–2010. Relapses mainly occurred in male infants infected with isolates with diminished antimicrobial susceptibility. Reinfections caused by isolates with the same serotype but different genotype were frequent, highlighting the need for genetic studies to differentiate among similar strains. In conclusion, the main change in pneumococcal AOM observed after the introduction of the PCV7 was the sharp decrease in vaccine serotypes. Also notable was the high burden of serotype 19A in total pneumococcal AOM before and especially after the introduction of the PCV7, as well as in relapses and reinfections.
Highlights
Acute otitis media (AOM) is one of the most common infections during childhood and nearly every child has experienced an episode of AOM by the age of 5 years [1,2]
Between 1999 and 2010, 1,006 non-duplicated S. pneumoniae isolates were cultured from the middle ear exudates collected from patients diagnosed with AOM
Compared with other bacteria causing AOM, S. pneumoniae otitis has been associated with more severe signs and symptoms and more complications [14]
Summary
Acute otitis media (AOM) is one of the most common infections during childhood and nearly every child has experienced an episode of AOM by the age of 5 years [1,2]. The etiology of AOM varies with age, the most frequently implicated agents being viruses such as rhinoviruses, influenza viruses, or respiratory syncytial viruses and bacteria, such as non-encapsulated Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. S. pneumoniae is one of the main agents causing bacterial AOM, directly or as complication of a viral upper respiratory tract infection [4]. Since the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) for the prevention of invasive pneumococcal disease, many researchers have demonstrated a reduction in AOM cases in vaccinated as well as in non-vaccinated children as a consequence of herd protection [2,5]. An increase in the proportion of AOM caused by non-vaccine serotypes, especially of serotype 19A, has been reported [5,6]
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