Increased in-hospital infections with increased temperatures

30 Oct

Knitted bacteria by loxosceles

An 8-year study of infection data from 132 hospitals finds that as outside temperatures rise, in-hospital infections with some of the most problematic pathogens rise also. – Wired.com

What just happened? The researchers looked at blood-samples from 132 US  hospitals (they admit that New England was somewhat lacking in representation) for 8 years, tracking the number of infections diagnosed as due to different kinds of bacteria.  It’s never normal to find bacteria in your blood, even normal flora of our bodies like E.Coli.

What were they looking for? They wanted to see whether the number of bacterial infections changed depending on the temperature outside (i.e. the season).

What’d they find? Well…

Independent of season, monthly humidity, monthly precipitation, and long-term trends, each 5.6°C (10°F) rise in mean monthly temperature corresponded to increases in Gram-negative bacterial BSI frequencies ranging between 3.5% for E. coli (95% CI 2.1–4.9) to 10.8% for Acinetobacter (95% CI 6.9–14.7). The same rise in mean monthly temperature corresponded to an increase of 2.2% in S. aureus BSI frequency (95% CI 1.3–3.2) but no significant change in Enterococcus BSI frequency. – Eber et. al (2011)

For every 5.6°C rise in monthly temperature, they increases in some bacterial infections and not others.

The ones they saw increases for are the Gram-negatives:

– E.Coli, which can cause a range of infections, from meningitis in young people to moderate diarrhea and dehydration, to extreme bloody diarrhea and widespread internal bleeding around your body.

– “Acinetobacter” or Actinobacter, which can cause pneumonia, or pus-filled cavities (abscesses) around your body if it gets systemic (i.e. into your blood).

Both of these bacteria are normally found on or in healthy people.  The trouble starts when it gets to where it shouldn’t get, and/or change so that they are more disease-causing.  That’s called “acquiring increased virulence” and it happens a lot in hospitals where you have lots of sick people and people who are always around sick people, and lots of antibiotic use.  Since there’s so much antibiotic use, bacteria in hospitals can more quickly develop antibiotic resistance which is something they can pass on to other bacteria.  Along with sharing antibiotic resistance, bacteria can share other virulence factors.

One of the more well known potentially antibiotic resistant bacteria, S.aureus, was also found to have increased numbers of infections as outdoor temperatures went up.  S. aureus resistance is pretty common now in both hospitals and out in the communities.  There are still treatments for most, but there are also strains of antibiotic S. aureus that don’t currently have any antibiotic that will consistently work.

No increase was observed for Enterococcus, which are bacteria that can cause GI problems like diarrhea, but can also cause troubles elsewhere once they get into the blood.

The bottom line? Bacteria become more dangerous as temperatures outside go up.  We’ve already seen that as temperatures go up, there are more infections.  The last paragraph of the paper sums the whole thing up (as they always do!):

In conclusion, we reported substantial increases in the frequencies of bloodstream infections due to clinically important Gram-negative organisms in summer months. These increases, as well as variations in infection frequencies within seasons, appear to be associated with elevated monthly outdoor temperatures. The seasonal trends reported may be used to inform infection prevention and should be considered in the design and evaluation of longitudinal quasi-experimental studies of infection prevention interventions. Furthermore, if the underlying mechanisms of the temperature associations are identified, these findings could inform the global climate change debate.

Emphasis mine.  Interesting!

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