In a time where there is increasing evidence that bacteria isolated from the urine of dogs and cats (and people!) is not always synonymous with a urinary tract infection, it can be increasingly confusing knowing when to reach for antibiotics. Hopefully the answers here will help clarify the current thinking on the management of bacteriuria.
What do we mean by subclinical bacteriuria?
Bacteriuria is defined as a positive urine culture in the absence of clinical signs of urinary tract disease. It has previously been referred to as ‘occult urinary tract infection’. Previously, cytological evidence of bacteria on urine sediment examinations has also been referred to as bacteriuria, but recent guidelines suggest this term should only be applied to positive urine cultures. While urine cytology may provide helpful contextual information, there can be discordant results between cytology and culture. Unhelpfully, quantitative culture cannot reliably distinguish subclinical bacteriuria from bacterial cystitis.
What is the prevalence of subclinical bacteriuria?
The prevalence of subclinical bacteriuria is relatively low amongst healthy canine populations (estimated 2.1-12%). The prevalence increases, however, in dogs with concurrent diseases such as diabetes mellitus and in dogs receiving immunosuppressant drug therapy.
Is treatment necessary for subclinical bacteriuria?
There is a wealth of evidence within human literature that supports the principle that antimicrobial treatment of subclinical bacteriuria is inappropriate, does not improve outcomes and is a major problem for antibiotic stewardship within the profession.
A recent study of 101 healthy female dogs documented bacteriuria in 9% however none of these dogs went on to develop cystitis where follow up (of three months) was available. (Wan et al., 2014).
Newly published guidelines from the International Society for Companion Animal Infectious Diseases (ISCAID) concludes that antimicrobial treatment for subclinical bacteriuria is ‘rarely indicated and is discouraged’. They also add that the finding of a multidrug resistant isolate should not affect the decision not to treat in subclinical cases as MDR isolates are not associated with more virulence and are not any more likely to cause clinical disease than broadly susceptible isolates.
Are there exceptions to this rule?
Antimicrobial treatment is still indicated in patients where subclinical bacteriuria is suspected to be a source of infection elsewhere in the body (e.g. discospondylitis).
Treatment should also be considered in dogs with imaging findings of significant urinary lesions (e.g. emphysematous cystitis, bladder TCC) or in patients potentially unable to exhibit lower urinary tract signs (e.g. due to paralysis).
Treatment of corynebacterium urealyticum (plaque-forming) or Staphylococci (urease-producing) should also be considered because of the inherent difficulty in treating associated encrusting cystitis and struvite urolith formation, respectively.
Patients who are due to have urological surgery or interventional radiology procedures (e.g. urolith removal, laser ablation of ectopic ureters) should also be treated 3-5 days prior to the planned procedure.
What about adjunctive urinary supplements (e.g. cranberry extract)?
There is currently no evidence to suggest the use of adjunctive treatments such as cranberry extract, probiotics etc is effective or necessary in the management of subclinical bacteriuria, however these supplements are well-tolerated and do not cause harm, thus there is no relative contraindication to these.
If we’re not going to treat subclinical bacteriuria, then should we at least monitor?
No, unless the dog develops clinical signs of bacterial cystitis; monitoring subclinical bacteriuria is unlikely to change treatment decision-making.
Well what defines bacterial cystitis?
The term bacterial cystitis (sporadic or recurrent) refers to cases of positive urine cultures and clinical signs of urinary tract disease (e.g. stranguria, pollakiuria). It was previously suggested that cytological evidence of lower urinary tract inflammation and a positive culture in the absence of urinary tract signs were also sufficient to make a diagnosis of bacterial cystitis however recent guidelines in both human and veterinary literature suggest this is no longer appropriate (and thus these cases should not be treated either).
The sensitivity of detection of lower urinary tract signs in dogs and cats however (where we are reliant on accurate history taking and many of our patients will not have physical exam abnormalities) is likely not comparable directly to people and this consideration should be balanced against antibiotic stewardship when deciding whether or not to treat patients without clinical signs (but with cytological evidence of inflammation).
References and further reading
Nicolle, L.E., 2014. Asymptomatic bacteriuria: Curr. Opin. Infect. Dis. 27, 90–96. https://doi.org/10.1097/QCO.0000000000000019
Wan, S.Y., Hartmann, F.A., Jooss, M.K., Viviano, K.R., 2014. Prevalence and clinical outcome of subclinical bacteriuria in female dogs. J. Am. Vet. Med. Assoc. 245, 106–112. https://doi.org/10.2460/javma.245.1.106
Weese, J.S., Blondeau, J., Boothe, D., Guardabassi, L.G., Gumley, N., Papich, M., Jessen, L.R., Lappin, M., Rankin, S., Westropp, J.L., Sykes, J., 2019. International
Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats. Vet. J. https://doi.org/10.1016/j.tvjl.2019.02.008
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