Daniel L. Chan

Background In spring 2021 increasing numbers of cats presenting with severe pancytopenia were noted in United Kingdom (UK). Objective To describe process and outcome of the investigation performed into the outbreak of pancytopenia in cats. Animals Five hundred and eighty client owned cats that presented with severe bi‐ or pancytopenia of unknown cause. Methods Real‐time data collection was performed by an online registration forum available to all veterinary surgeons in UK. Data collected included demographics, clinicopathological findings, diagnostic testing, dietary and drug history, outcome and COVID household status. Mycotoxicological feed analysis was performed on feed samples of 3 diets frequently mentioned in the database and 3 control diets. Results Five hundred and eighty cats presented to 378 veterinary practices were included for analysis. Case fatality rate was 63.3%. Dietary history was available for 544 (93.8%) cats, of which 500 (86%) were fed 1 of 3 diets (which were recalled midinvestigation). 54 (9.3%) cats were not fed a recalled product, with diet information unknown in 26 (4.5%) cats. Analysis of feed samples revealed concentrations of hematotoxic trichothecene T‐2/HT‐2 mycotoxins greater than recommended by the European Commission in 5/7 recalled diet samples but in none of control diet samples. The trichothecene mycotoxin diacetoxyscirpenol (DAS) was detectable in all recalled diet samples but not in any of control samples. Conclusion and Clinical Importance Contaminated‐feed induced trichothecene mycotoxicosis should be considered as a differential diagnosis for pancytopenia in cats.