A case of persistent IgE sensitisation almost two decades following ampicillin anaphylaxis.

BACKGROUND: Although most immunoglobulin E (IgE)-mediated penicillin allergy wanes with time, sensitisation may occasionally persist for many years. Previous reports on the loss of penicillin-specific IgE sensitisation were based on non-anaphylaxis cases and, although uncommon, persistent sensitisation may still be possible in the minority of cases. OBJECTIVE: This case highlights that irrespective of the elapsed duration since the index reaction, it is important to remain vigilant when approaching patients with a history of severe reactions. MATERIAL AND METHODS: We described a case of persistent IgE sensitisation almost two decades following ampicillin anaphylaxis. RESULTS: A 78-year-old male with a history of perioperative penicillin anaphylaxis in 2003 was referred for allergy workup in 2022 before his knee joint replacement surgery. The patient had strictly avoided all beta-lactams since the index reaction. However, his penicillin-specific sensitisation persisted, evidenced by positive skin tests (with generalised urticaria after intradermal testing) and basophil activation tests. CONCLUSION: To our knowledge, this was the first case of positive BAT tested around two decades following the index reaction. This case illustrates that a cautious approach may still be warranted in patients with a history of severe reaction to penicillin regardless of the duration since the reported index reaction.

Piperacillin-Tazobactam Allergies: An Exception to Usual Penicillin Allergy.

PURPOSE: The majority of penicillin allergy labels are false, and skin tests (ST) have high negative predictive value (NPV) of up to 90%. Piperacillin-tazobactam (PT) allergy has been suspected to be an exception to this, but existing literature is scarce. We investigate the epidemiology, clinical characteristics, testing outcomes and predictive value of ST in patients referred for suspected PT allergies. METHODS: The records of all patients referred for suspected PT allergy testing and prescription rates of PT in all Hong Kong public hospitals (2015-2019) were analyzed. RESULTS: There was an increase in both PT prescriptions and number of newly reported PT allergies between 2015 and 2019. The majority (91.1%) of patients with suspected PT allergy had at least 1 underlying medical co-morbidity or immunosuppressant use leading to increased risk of infections. Thirty-six patients with suspected PT allergy completed ST. Two patients had positive ST, and 32/34 patients with negative ST underwent drug provocation testing (DPT). Nine of these patients were diagnosed with PT allergy based on positive DPT. Overall, 11/34 (32.4%) were diagnosed with PT allergy and the NPV of ST was 71.9%. CONCLUSIONS: There is growing utilization of PT and corresponding cases of suspected allergies. The majority of suspected PT allergies had increased risk for recurrent infections. Unlike other penicillin allergy, there is a high rate of genuine PT allergy (up to 30%) and a poor NPV of ST (up to 70%). DPT remains the gold standard for accurate diagnosis, and all patients with a suspected allergy should undergo thorough allergy workup.