Recorded penicillin allergy linked to increased risk of ‘superbug’ infections

Patients who are documented as being allergic to penicillin are at a higher risk of developing ‘superbug’ infections MRSA and healthcare-associated infection C difficile, according to a new study.
 
To evaluate the public health consequences of a penicillin allergy label, researchers at Massachusetts General Hospital in the US examined the relation between penicillin allergy and development of MRSA and C difficile.
 
Published in The BMJ journal, the research looked at the records of 301,399 adults in the UK general practice from 1995 to 2015.
 
The researchers said penicillin allergy is the most commonly documented drug allergy, reported by about 10% of patients. However, previous studies have shown that more than 90% of patients with listed penicillin allergies can be safely treated with penicillins. Most patients with a documented penicillin allergy are not allergic – that is, there is no immediate hypersensitivity. After evaluation by an allergist, about 95% of patients with reported penicillin allergies were found to be penicillin tolerant.
 
The discrepancy between labelled and confirmed penicillin allergy stems from misdiagnosis, such as a viral exanthema is misinterpreted as an allergy; misassumptions, where an intolerance, such as a headache, is listed as an allergy; and remote timing of the allergy evaluation, since 80% of patients with immediate hypersensitivity to penicillin are no longer allergic after 10 years.
 
Researchers say most patients with a penicillin allergy label therefore unnecessarily avoid penicillins.
 
Using data from The Health Improvement Network (THIN), an electronic medical record database of 11 million UK patients, researchers identified 64,141 adults with a documented penicillin allergy and 237,258 matched adults of similar age and sex with recent penicillin exposure but without a penicillin allergy.
 
None of the participants had any history of MRSA and C difficile infection, and were followed up for an average of six years, during which time use of antibiotics and cases of doctor-diagnosed MRSA and C difficile were recorded.
 
A total of 1345 participants developed MRSA and 1688 developed C difficile over the follow-up period.
 
After adjusting for several known risk factors, the researchers found that a penicillin allergy label was associated with a 69% increased risk of MRSA and a 26% increased risk of C difficile.
 
The risk is largely due to the use of more ‘broad spectrum’ antibiotics as alternatives to penicillin, which may be fuelling the development of drug-resistant bacteria.
 
The researchers argue that addressing penicillin allergies ‘may be an important public health strategy to reduce the incidence of MRSA and C difficile among patients with a penicillin allergy label’.
 
They note that evaluation of penicillin allergy often involves a skin test and, if the result is negative, a challenge dose of penicillin or amoxicillin is administered under medical observation.
 
Dr Evan Ackermann, GP and Chair of the RACGP Expert Committee – Quality Care (REC–QC), told newsGP that the results are not unexpected.
 
‘This is one of the issues that the RACGP has been addressing,’ Dr Ackermann said.
 
‘[We are] looking at antibiotics and antibiotics use because there is a national-wide issue about antimicrobial stewardship and the increase of resistance bacteria in the community.’
 
Dr Ackermann said a lot of people who believe they have a penicillin allergy actually lose their allergy with time.
 
‘A lot of the time it was inadequate or inappropriate documentation … usually they get a sore throat, a viral infection, they are given some antibiotic, they develop a rash. A lot of the time it’s just a viral infection from the start and they get a viral rash, and it’s inappropriately given that it is the penicillin causing the rash,’ he said.
 
‘And it is because people with a known penicillin allergy do get a lot of alternative medication or alternative broad spectrum antibiotics that we see increased rates of clostridium difficile and MRSA.’
 
However, Dr Ackermann said, for those with a recorded penicillin allergy, the increase in susceptibility to the two superbugs in absolute rate, as opposed to comparative rate, is quite low.
 
‘For most practices it is probably not going to prompt a change … not worth going out and checking everyone’s penicillin allergy,’ he said.
 
‘Where this might come in and be effective is for those patients who are likely to be chronic long-term antibiotic users.
 
‘That might be where they have got long-term infections or where they are predisposed to long-term infections – the chronic obstructive airways of people with cystic fibrosis – people who have got long-term conditions that would most likely result in chronic, repeated antibiotic use.
 
‘If they have a penicillin allergy, it might be worth finding out if that’s a real allergy.’
 
Dr Ackermann said the best strategy is to try and minimise the use of antibiotics.
 
‘There are certain key areas where we can reduce antibiotic use,’ he said. ‘If you do have an infection that you have to treat, follow the antibiotic guidelines and prescribe the narrowest-spectrum antibiotic that you can.’

antimicrobial stewardship infection C difficile MRSA penicillin superbug