Age and Sex
The MR was (not surprisingly) low during the 1st 5 age categories (<400 deaths per 10,000 CYAR) and reaching over 1,600 deaths per 10,000 CYAR in age category 11 <12 years. By diagnostic category, urinary, neoplastic, and cardiovascular (nonsignificantly [NS] judged by overlapping CIs) and gastrointestinal (NS) increased with age whereas infections and traumatic causes (NS) decreased with age. Most of these results are similar to clinical perceptions or, where relevant comparisons can be made, published results from dogs. Case series based on pathology data show that infections and trauma are the most common causes of death in cats.3,4 Traumatic road accidents have been shown to decrease in frequency with increasing age.10 Data from studies presenting proportional mortality figures suggest that young cats often die from infections, whereas this is less common for older animals.3,4,11 No significant differences were found between sex for the overall ASMRs. Unfortunately, data on deaths in cats over 13 years were not recorded. Cats can have veterinary care insurance until older ages and analysis of that data may shed some light on diseases affecting older cats. However, from the perspective of preventing premature death, the mortality in the “youngest” cats (ie, <13 years of age) is undoubtedly of the highest importance.
At 5, 7.5, and 10 years of age, many breeds showed a decrease in mortality over time (based on nonoverlapping CIs between time periods). However, in Ragdolls there are no differences and in Maine Coons the CIs clearly overlap. As none of the survival curves reach 50% even in the highest age category, it is evident that that median age of death in these life-insured cats is >12 years of age.
Breed-specific mortality varied from 664 in the Siamese to 285 deaths per 10,000 CYAR in the Bengalese (Table 1). In particular for the breed-specific analysis, the MRs were age standardized to avoid the effect of differing age distributions, as caused by waxing and waning popularities for some breeds, or changes in insurance enrollment. Domestic cats have an ASMR just below the average mean. In this database, the domestic cats may differ from the total population of domestic cats in Sweden. From the survival analysis of the more common breeds, Siamese and Ragdolls have the lowest survival to 10 years.
Population-based research on these insurance data is facilitated by the mandatory use of a standardized, hierarchical diagnostic registry by all contributing veterinarians.7,12 Previous studies have validated the accuracy of the diagnostic information for dog and cat data.13 In the cats, we found that both demographic (breed, sex, and year of birth) and diagnostic information was correctly coded in ≥89% of the cases. However, we are unable to determine the level of certainty of the veterinarians' diagnoses, or the amount of ancillary information that underlies the diagnosis (eg, whether specific-neoplasia diagnoses are based on histologic confirmation or not). However, the use of diagnostic categories allows us to group the data at levels for which we are more confident in the validity of the information.
“Dead no diagnosis” has been shown to be one of the most common recorded “causes” of death in these cats, as has been seen in studies of dogs and horses. This likely is a reflection of the realities of veterinary practice where cautious veterinarians are unable or unwilling to commit to a specific diagnosis in the absence of a diagnostic evaluation. There might also be a tendency to use a nonspecific code for convenience. However, certain categories of disease (eg, heart failure) might be more likely to be “missed” and placed in the no diagnosis category because of lack of diagnostic evaluation or postmortem examination than cases of, for example, traumatic death. Space does not allow a detailed discussion of all of the major diagnostic categories for deaths in these cats and we have chosen to highlight the 5 most common specific categories.
Although CIs have been calculated, their interpretation is difficult. These data essentially represent a census of deaths in the complete population of life-insured cats. In the subsequent discussions we have therefore chosen to focus on the point estimates in discussing differences. Extrapolation and generalization of these findings to other populations of cats should be done with extreme caution. In addition, readers may note that the CIs for the ASMRs become considerably wider than CIs of raw rates (unpublished information).
Urinary disease was the most common cause of death in total and in the Persians, British shorthair, and Ragdolls. In the 8 breeds in Figure 4, only the Ragdolls had a very high ASMR for urinary problems. The main 2 categories within “urinary” are kidney/ureter and lower urinary problems, with the former, having an ASMR approximately 3 times the latter. The Persian group had a considerably higher ASMR for urinary disease than the domestics. Within this breed, polycystic kidney disease accounted for a proportional mortality within the diagnostic category urinary of 20% and the Persian group actually does have a somewhat higher proportion of upper compared with lower urinary disease compared with the other breeds. Accordingly, only a part of the high rate is likely because of the known predisposition for polycystic kidney disease.14 As death because of urinary disease increases with age, it can be assumed that it will be a common cause of death in these breeds also after 12 years of age.
Traumatic causes of death were primarily traffic accidents and falls from a height, and were most common in domestic cats, Norwegian Forest cats, and Maine Coons. This may be a reflection of the degree to which these breeds have access to the outdoors, and be opposite to the situation postulated for urinary deaths10 (ie, indoor cats tend to get obese or develop disease because of lack of exercise but are less at risk for severe trauma). In 25% of Swedish breeding catteries, some or all of the cats had free access to outdoors.15
Neoplastic disorders are the 3rd most common cause, with considerable variation among breeds. For the Maine Coon and Siamese groups, neoplastic disease, dominated by mammary tumors in the Siamese, was the most common cause of death, even though these are relatively young cats. Significant breed differences in cancer risk are described for dogs, and a genetic component exists for some cancers in dogs. Studies have shown that Siamese cats are at increased risk of developing mammary carcinoma, although the mechanism is unknown.16
In the total population, infectious disease was the most common cause of death. This is probably because all cats must be vaccinated against feline panleukopenia before enrollment into life insurance. Domestic and Maine Coon cats had low MRs attributed to infections compared with several other breeds. Infections, dominated by FIP, were the most common cause of death in Birmans. FIP is a sporadic disease caused by mutation of an endemic virus (feline coronavirus, FCoV).17 Inheritance of susceptibility to FIP previously has been described for Persians and Birmans,17 and an overrepresentation of other breeds also has been described.17 As cats would not be covered for death because of FIP occurring within a year after the start of insurance, and because FIP can be challenging to confirm,17 the number of FIP cases may be even higher than shown here. Regardless, infections dominated by FIP were the most common diseases in Birmans up to 12 years of age. One contributing factor to the high incidence of infections in Birmans may be that a number of cats with ascites or hydrothorax because of restrictive cardiomyopathy are falsely diagnosed as having exudative FIP. Death because of cardiovascular reasons was the 3rd most common cause in Birmans, and these diagnoses can be difficult to differentiate without further clinical testing, such as echocardiography.18
The most common specific diagnosis within the cardiovascular category was, not surprisingly, cardiomyopathy. However, feline cardiomyopathies are a heterogenous group of diagnoses. Depending on the morphologic appearance and pathophysiology, cardiomyopathy in cats is frequently classified as hypertrophic, dilated, restrictive, arrhythmogenic, and “unclassified” cardiomyopathy.18,19 The specific-feline cardiomyopathy often was not specified in the database, but based on the literature and clinical experience, hypertrophic cardiomyopathy, was the most likely diagnosis in most of the cases in most of the breeds. This disease is well documented in almost all of the breed groups in this study as a major contributor to cardiovascular disease.19,20 The present study could not show a difference in sex, which is in agreement with previous studies.20 The domestic cat group stands out as having a lower cardiovascular ASMR than other breeds. This finding may not completely reflect the true incidence of cardiomyopathy in this population because domestic cat owners may not be as motivated as pure bred cat owners or breeders to establish an exact diagnosis or to treat chronic disease.
We have closely considered whether the interesting result on survival (ie, the increase over this 8-year period for cats <13 years of age) could have arisen as a consequence of insurance policies or been a function of the research method. However, we found both of these unlikely to account for the magnitude of the differences seen. As regards statistics, given that the method is stratified on and uses the available information at each age span to calculate the statistics, if there were no cats or deaths in an interval (ie, “young”), problems may arise at older ages, but this was not the case here. It is anecdotally assumed that owners are more willing to access veterinary care for their cats and to engage in treatment for chronic diseases (eg, diabetes) than was the case in the past. Presumably, increased access to veterinary care would be facilitated by having health care insurance (which almost all life-insured cats have). A similar pattern of decreased mortality over time has been shown in dog data from the Agria database (Brenda Bonnett, personal communication). The extent to which increased survival can be attributed to veterinary care per se or to the attitudes of owners with regard to willingness to treat older animals and those with chronic disease is impossible to determine based on our results.
With regard to the whole population (however, not between breeds, see breed section above) the yearly MRs (data not shown) and the ASMRs were similar. Reasons for varying overall rates over the years include random variation, varying breed-age distributions (in the unadjusted rates) and undefined systematic variation relative to the insurance process or other factors.