Health care use and serious infection prevalence associated with penicillin “allergy” in hospitalised patients: a cohort study.
What is it all about?
What did they do?
Once the cohorts had been created, information from the record system was used to find the outcome measures of:
- Hospital length of stay (primary outcome)
- Antibiotic courses used
- Rates of C. Difficile, MRSA and VRE infection
What did they find?
When looking at their primary outcome, having a penicillin allergy label added 0.59 (95% CI 0.47-0.71) days to the hospital stay, being slightly more if you were female (0.68) compared to male (0.35).
The analysis of antibiotic prescription was a little harder to unpick. The ‘top 10’ list of antibiotics used showed that there was an increased use of ciprofloxacin, vancomycin and clindamycin in the allergy-label group compared to the matched controls. The increased rate of fluoroquinolones was quite notably significant at 25.3% vs 14.3% (p<0.00001). However, there wasn’t a huge use of penicillins in the control group, with other differences seeming to be made up by an increased rate of first-generation cephalosporins in the control group, and a smaller increased rate of third-generation cephalosporins.
Finally, the results for the prevalence of the specific infections were perhaps the most intriguing. In their results they noted that having a penicillin allergy label resulted in a risk ratio for C. Difficile of 1.234 (95% CI 1.156-1.317), for MRSA of 1.141 (1.071-1.317) and VRE of 1.301 (1.125-1.504). Interesting.
Is it any good?
In terms of problems with the study, I always have a little bit of concern about the patient selection in this type of study. The database they have worked with is from a single insurer, and I wonder what possible biases might arise from this starting point, especially as this American healthcare model is less well known to me. Is there a selection bias for patients here? Are there subtle financial incentives that might be unconsciously present, for example, around antibiotic prescribing? I don’t feel that I know the system well enough to understand how representative this cohort will therefore be. I feel similarly about the whole process of matching patients to a control, and especially when in this case they decided to match each case to two control patients without actually saying why. Did a one-to-one match not give as exciting results? If this matching process isn’t really explicit in its methods then it leaves me a little suspicious about possible statistical trickery.
Overall I think the study raises some very interesting questions, though I am not sure we can be completely confident about the conclusions that the authors have drawn. There does seem to be a difference in some quite important clinical outcomes, and the data would point towards the allergy label being a possible cause. This seems plausible, as there does seem to be a difference in prescribing practices of antibiotics between the two groups, and it would seem that the choice of antibiotics in the ‘allergy’ cohort C.Difficile-ogenic, for instance. However, as the authors note, the explanation for the MRSA incidence doesn’t have a clear mechanism, and perhaps the conclusions the authors are trying to draw aren’t any better supported than the conclusion that being allergic to stuff increases your risk of medical complications. That being said, the difference between reported and actual penicillin allergy that the authors describe (just 2% actually having a true allergy!) suggests that in may be the label in itself, rather than an actual impact of allergy. As such, I am more drawn to their conclusion that the widespread acceptance of ‘allergy’ labels could be resulting in harm to patients.
Well thanks for reading. I hope this article has, at the very least, got you even more interested in the upcoming DALES project. This paper has really got me wondering more about how the difference between allergy and intolerance may be more important to elucidate than it might first appear. Given how common this is in our daily practice, I am intrigued to find out more. So please let me know your thoughts and check out the websites below. Hopefully have another post coming soon to follow up on this theme further.
NWRAG - www.nwrag.co.uk
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