Limitations of using feline coronavirus spike protein gene mutations to diagnose feline infectious peritonitis

Barker, Emily N.; Stranieri, Angelica; Helps, Chris R.; Porter, Emily L.; Davidson, Andrew D.; Day, Michael J.; Knowles, Toby; Kipar, Anja; Tasker, Séverine

Data [comprising: cat identification number; age; diagnosis (with FIP vs without FIP); sample type (tissue, fluid and faeces) and specific organ/body cavity of origin where applicable; histopathology result (absence vs. presence of changes consistent with FIP); IHC result (absence vs. presence of FCoV antigen in lesions); FCoV RT-qPCR result; relative FCoV copy number; S protein mutation analysis result (non-mutated vs mutated vs serotype 2 vs. failed)] were entered into a database (Excel 2008, Microsoft; Additional file 1) and exported into IBM SPSS Statistics software (version 23.0). Continuous variables within the data sets were evaluated for normal distribution using the Kolmogorov-Smirnov test. Non-normally distributed data were described as median and range (minimum and maximum values). Population proportions were compared using Chi squared test. Data evaluating FCoV relative copy numbers in tissue and faecal samples from cats with and without FIP were analysed using a multilevel modelling approach (MLwiN v3) [28] to account for the repeated measures within cats. An alternative, simplified analysis was also employed in which non-parametric Mann-Whitney U tests were used to test for differences between cats on the individual measurements. The conclusions drawn from both analyses were in full agreement (data not shown), so the simpler Mann-Whitney U test analysis is presented here. Relative copy numbers were compared between the cats with FIP and cats without FIP for different sample types (tissue, fluid and faeces). Significance was assigned at a level of p < 0.05.