What are the Most Common Germs Causing Pediatric Ear Infections? Implications for Antibiotic Selection.

Ear infections rank as one of the most common infections of childhood. Pretty much every kid suffers from ear infections whether a few or more times a year usually until about age 5-6 years when the frequency starts to drop off.

Although there are the standard antibiotics that pediatricians prescribe to treat ear infections, it is based on certain assumptions on what exactly is causing it. Assumptions that sometimes ends up being incorrect resulting in multiple courses of antibiotics.

So what are the most common germs that cause ear infections? Prior to the introduction of the prevnar vaccine for kids (part of the childhood vaccine series) starting in 2000 with an updated version in 2010, the culprit germs causing ear infections were typically poly-microbial in nature involving Haemophilus influenza, Streptococcus pneumoniae, Alloiococcus otitides, and/or Moraxella catarrhalis.  

Based on a 2015 research paper which re-examined this question after the year 2010 introduction of the updated prevnar vaccine, the most common organisms isolated from ear infections narrowed down to just two: Haemophilus influenza and Moraxella catarrhalis. If ear infection fluid is not purulent in nature, the most common germ then becomes Alloiococcus otitides. And instead of being poly-microbial ear infections, these ear infections typically were caused by only one infectious agent. Other germs were certainly present, but the prevalence decreased significantly.

The key take home point is that Streptococcus pneumoniae which used to be one of the most common causes of childhood ear infections is no longer the case and this is felt to be directly attributable to the prevnar vaccine. 

The second point is that amoxicillin, which is a commonly prescribed antibiotic to treat ear infections, is most effective against gram positive organisms like Streptococcus pneumoniae. However, with the decline of Streptococcus pneumoniae since 2010, amoxicillin may not be the best antibiotic to use now since Haemophilus influenza and Moraxella catarrhalis which are gram negative organisms are the more prevalent. Antibiotics that work best against these gram negative organisms include trimethoprim-sulfamethoxazole, cefuroxime axetil, cefixime, clarithromycin, azithromycin, and fluoroquinolones. Fluoroquinolones should only be given as ear drops and not orally in kids. 

What I find curious is why Haemophilus influenza is still a common organism in ear infections at this time. As part of the childhood vaccine series, the vaccine Hiberix (started being given in 1985) specifically targets this germ. Although epiglottitis and meningitis (caused by Haemophilus influenza) has mostly disappeared with this vaccine, I would have also thought it should have disappeared as a cause for ear infections as well.

Reference:

Otopathogens Detected in Middle Ear Fluid Obtained during Tympanostomy Tube Insertion: Contrasting Purulent and Non- Purulent Effusions. PLoS ONE 10(6): e0128606. doi:10.1371/journal.pone.0128606