Results showed that the interaction was not significant for pairs involving FIV. All other pairs (FHV-FCV, FHV-FPV and FCV-FPV) were found to interact, i.e., the number of individuals coinfected by two viruses could not be explained by shared risk factors. The three significant associations were all positive, meaning that there were always more co-infected individuals than expected considering shared risk factors (Table 3) .