Prevalence of adults labelled as allergic to penicillin in an urban health centre

Dear Editor,

The true prevalence of penicillin allergy remains unknown. Self-reported rates tend to be high; although we lack national data, in countries such as the United States or Australia, up to 10% of the population claim to be allergic. However, when properly assessed, only a small percentage of these cases (approximately 5%) are confirmed. This discrepancy is due, among other factors, to the natural loss of drug sensitivity over time, as well as frequent mislabelling of adverse reactions that are not related to hypersensitivity reactions.^1,2

Accurate characterisation, documentation and investigation of drug-related reactions is essential. Allergy testing is complex and traditionally involves skin testing with the suspected drug, followed, if negative, by an oral challenge test. As it is not feasible to study all individuals labelled as allergic, current trends advocate simplification: false allergy labels should be removed, and in patients deemed low-risk, a direct oral challenge without prior skin testing is considered a safe and dependable approach.³

The aim of this study was to determine the prevalence of self-reported penicillin allergy among adults assigned to an urban health centre in Health Area V (Asturias, Spain). Secondary objectives included estimating the proportion of potentially false labels and the proportion of patients with a low risk of allergic reaction among those reporting penicillin allergy.

A simple random sample was drawn from the adult population (≥18 years) registered at Natahoyo-Tremañes Health Centre (488 individuals from a total of 16,636). A bespoke questionnaire was administered via telephone interview, following verbal informed consent. Participants were asked about drug allergies, the implicated medication, and the characteristics of the reaction(s). In cases of reported allergy to penicillin or other beta-lactams, the clinical risk was assessed using the PEN-FAST tool.⁴

A total of 408 individuals participated (83.6% of the sample). Among them, 18.38% (95% CI: 14.50–22.26%) reported being allergic to at least one drug, with significant sex-related differences: 23% of women reported some form of drug allergy compared with 13.5% of men.

Penicillin was the most commonly reported allergen, accounting for 5.64% (95% CI: 3.28–8.00%) of the total sample.

Cutaneous symptoms, either alone or combined with other manifestations, were the most common presentation (43.47%). Table 1 details manifestations and risk of reaction.

Table 1.

Manifestation and risk of reaction in adults labelled as allergic to penicillin.

Clinical manifestations reported
Manifestation	Frequency	Percentage
Skin symptoms, alone or with other symptoms	10	43.47%
Skin symptoms alone	6	26.08%
Angioedema	5	21.73%
Respiratory distress	1	4.34%
Anaphylactic shock	1	4.34%
Gastrointestinal: vomiting, diarrhoea	4	17.39%
Candidiasis	2	8.69%
Dizziness	1	4.34%
No s/No c	3	13.04%

Risk of reaction in penicillin-allergic individuals according to the PEN-FAST criteria
Classification	Points	Frequency	Percentage
Very low risk	0 points	4	17.39%
Low risk	1−2 points	13	56.52%
Moderate risk	3 points	6	26.08%
High risk	4−5 points	0	0%

According to the PEN-FAST score, 73.9% of those who reported penicillin allergy were at very low or low risk of true allergic reaction. In 30.44% of cases (95% CI: 13.21–52.92%), the reported reactions met the criteria for potentially false labelling.

The prevalence of self-reported penicillin allergy in our study was 5.6% (95% CI: 3.28–8.00%), lower than the 10% reported in other studies^1,2; although the figures are highly variable according to the populations studied.³ The value of our study lies in the fact that our data are drawn from the general population, which is underrepresented in other prevalence studies.

Regarding the manifestations described by those labelled as allergic to penicillin, 3 out of 10 reported reactions that did not meet the criteria for immunologically mediated responses (i.e., they lacked sudden symptom onset or typical cutaneous or allergy-related symptoms) and were compatible with false labelling. The symptoms were mainly consistent with gastrointestinal side effects or alterations to the microbiota. It is now recommended that such labels be removed without further investigation.^1,2,5

Excluding those considered false labels, the remaining individuals with some form of low-risk allergic manifestation could be suitable candidates for direct oral challenge testing.⁵ It has even been proposed that such testing for low-risk patients could be conducted at the primary care level.⁵

Ethical considerations

The study was conducted according to the guidelines of the Declaration of Helsinki and was approved by the Ethics Committee of the Principality of Asturias in April 2024.

Funding

This study has not received any funding.