ISCAID Guidelines & management of bacterial urinary tract infections in dogs & cats: Part 2 | VETgirl Veterinary Continuing Education Podcasts
In today’s VETgirl online veterinary continuing education podcast, we’ll review the latest guidelines for a condition we see just about every day in the vet hospital – urinary tract infections (UTIs). This is based off the most current International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats . This is a 2-part podcast, so check out last week’s episode for Part 1!
I’m sure that, like me, you all have your own way of working these up and treating them on a case by case basis. But with antimicrobial resistance on the rise in both human and veterinary medicine, we can benefit from guidelines such as these to help modify our practices and hopefully limit any overuse of antimicrobials. Keep in mind that these guidelines, while meant to help us with the majority of our cases, are by no means meant to be the only way to practice. There are so many considerations in each case that we will be reviewing – like has the animal already had recurrent infections? Are there stones present that can be fostering bacteria? Are there rules in place for prophylactic and empiric use of antibiotics? So, we will be summarizing these rather long guidelines in hopes of streamlining our diagnostic approach and treatment of various urinary tract infections in the cat and dog.
These guidelines are the latest updated revision of similar guidelines put out by the Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Disease. It’s likely that these guidelines will continue to be adjusted over time as newer high-level studies are conducted in regards to veterinary antimicrobial usage for urinary tract infections. At present, these guidelines reflect information obtained from both human and veterinary studies and anecdotal information.
In regions with high rates of castration, bacterial prostatitis is relatively uncommon. Any time bacterial cystitis or subclinical bacteriuria are identified in the intact male dog, the clinician should investigate for bacterial prostatitis. Diagnostics should include a physical examination with rectal palpation of the prostate, CBC, biochemistry profile, urinalysis, urine culture with urine collected via cystocentesis, and ultrasound imaging of the prostate. Most commonly, diagnosis of bacterial prostatitis is achieved from a combination of clinical signs, positive urine culture, and ultrasound imaging. As an alternative to urine cultures, the third fraction of ejaculate, or prostatic fluids from prostatic massage or FNA of the prostate can be cultured. Prostatic aspirates and biopsies should be cultured, and submitted for cytologic review or histopathologic review to screen for neoplasia. Urine cultures and prostate fluid cultures can produce differing results since prostatic fluid can normally have some bacteria in it. Aerobic culture should grow out most of the prostate bacterium, but there’s a low incidence of infections with Mycoplasma and Ureaplasma. In addition to cultures, if the dog is to be used for breeding purposes, serologic testing for B. canis is recommended. Prostatic abscesses have poor rates of resolution when medically managed so they should be drained percutaneously with ultrasound guidance or surgically lanced. These guidelines recommend first culturing urine or prostate fluid or prostate FNAs in order to provide instant and appropriate medical management following drainage or surgical lancing of prostatic abscesses. If the pet is not to be used for breeding, castration is recommended as soon as possible.
One of the greatest challenges in treating these cases is that the prostate is a very tough organ for antimicrobials to diffuse into! Drugs with a higher lipid solubility and higher pH may be able to cross the blood-prostate barrier most effectively. A good first-line empiric antimicrobial for the prostate is a fluoroquinolone. That being said, ciprofloxacin is not recommended due to poor prostatic tissue penetration compared to enrofloxacin and because the bioavailability of this drug in dogs is unpredictable. TMS may also be a good empiric antimicrobial though only the trimethoprim component has good tissue penetration in the prostate. Clindamycin and macrolides can penetrate the prostate, but they have no gram-negative efficacy so should only be used based on culture results. Even though there may be increased tissue penetration in the case of prostatitis due to a breakdown in the tissue barrier from inflammation, empiric use of penicillin, cephalosporins, aminoglycosides and tetracyclines should be avoided. Chloramphenicol has decreased tissue penetration in the prostate, but can still be an effective choice based on culture results. For infections that are resistant to fluoroquinolones, TMS, clindamycin, and chloramphenicol, the clinician should consult with a theriogenologist, veterinary microbiologist, veterinary internist, or a veterinary pharmacologist. No conclusions were made in these guidelines on the most appropriate duration of antimicrobial therapy for prostatitis, which may be anywhere between 4-12 weeks. Four weeks is the most common for acute infections and 4-6 weeks is more common for chronic infections. A recheck ultrasound should be performed 8-12 weeks after treatment is complete. If the patient fails to respond to initial treatment, then further diagnostics should be performed such as an FNA of the prostate if it hasn’t been already done. It is also reasonable to consider switching the antimicrobial to another empiric antimicrobial that is in a different drug class and reassessing for clinical response. Culturing for the purpose of guiding medical treatment of prostatitis is not recommended.
Walking into my ICU, you will see a handful of patients with urinary catheters attached to closed collection systems. Urinary catheters are utilized in the medical management of many conditions such as urinary tract obstructions, kidney failure, and in patients with decreased mobility or paralysis. We know that these urinary catheters can be a source of urinary tract infections from bacteria on the outside of the catheter or in the lumen of the catheter that migrates or is accidentally flushed back up into the bladder. In humans, the greatest risk factor for a urinary catheter associated UTI is the duration of catheterization. Our own veterinary studies show a prevalence of 10-55% for bacteriuria in catheterized dogs and cats. We can take some precautions to help minimize the risk of catheter-associated urinary tract infections such as using aseptic technique when placing and managing urinary catheters, using closed collection systems (be sure to attach those red rubber catheters or tom cat catheters to closed collection systems so they are no longer open to the environment), inspecting the urinary catheter routinely for kinks, blockages, or debris on the outside or inside, removing the urinary catheter as soon as the patient’s condition is stable enough, and using intermittent urinary catheterization instead of an indwelling urinary catheter when possible. Some hospitals use the antibacterial coated urinary catheters. At this time, veterinary research does not support or prohibit their use, so these are a reasonable consideration.
Diagnosing a UTI while the patient has a urinary catheter in place can be a bit tricky. Routine screening of the urine from a urinary catheter for cytologic review is not recommended due to the likelihood of finding contamination in the catheter. If the patient develops a fever or if there is a change in urine odor or appearance while a urinary catheter is in place, it is reasonable to investigate for infection. If bacterial cystitis is suspected, the urinary catheter should be removed, a cystocentesis performed for culture submission, and a new urinary catheter replaced, if it is still needed. For cases where you really can’t risk or perform cystocentesis, you can place a new, sterile urinary catheter, remove and discard the first 3-5mL of urine, and then collect your urine sample for culture. A urine culture should never be performed from urine sitting in the urine bag or sitting elsewhere in the collection system. Positive urine cultures should be treated with either short course (3-5 days) of antimicrobials for sporadic bacterial cystitis, or longer (7-14 days) for recurrent urinary tract infections. If bacteriuria is identified during hospitalization, but the patient is not exhibiting clinical signs attributed to a UTI, then there is no need to treat and no need to remove or to replace the urinary catheter. When it is time to remove the urinary catheter, it is not recommended to culture the catheter tip because they have been found to be colonized about half the time, but the clinical significance isn’t clear. Likewise, culturing a urine sample upon catheter removal is not indicated. Prophylactic antibiotics either during maintenance of an indwelling urinary catheter or after removing a urinary catheter are not recommended.
Examples of urinary procedures where we need to consider our judicious use of antimicrobials include cystoscopic procedures (biopsies, laser lithotripsy), urethrotomy, urethrostomy, urethral and ureteral stent placement, voiding urohydropropulsion to remove urethral stones, and subcutaneous ureteral bypass placement. Sources of infection for urinary procedures in cats and dogs include the skin, vagina, and rectum. For all cystoscopic, laparoscopic, or surgical procedures that will manipulate the urinary tract, the recommendation is to obtain a urine culture from urine collected via cystocentesis. Identified infections should be treated for 3-5 days before procedures are performed for the purpose of reducing and/or eliminating bacteria. For procedures that do not involve surgical entry into the urinary tract, peri-operative antimicrobials are only indicated if pre-procedure testing shows bacteriuria or positive urine cultures. Peri-operative antimicrobial therapy should include a 1st or 2nd generation cephalosporin administered intravenously within 60 minutes of the start of procedure, repeated dosing every 2 half-lives, and then stopping at the cessation of the procedure. Continued use of antimicrobials after the procedure should only be used on a case by case basis depending on urine culture results obtained prior to the procedure. If clinical signs of bacterial cystitis continue after the procedure, a repeat urine culture should be performed. Any infection should be addressed with medication, but if the culture is negative then the clinician should investigate for other causes of the clinical signs. For any surgery involving the urinary tract, peri-operative antibiotics are indicated even if pre-surgical cultures are negative. If patients develop post-operative infections with Enterococcus species, they should receive an aminoglycoside (when not contraindicated by patient’s renal function) and either ampicillin or cefazolin.
Medical Dissolution of Uroliths
The last condition we are going to discuss in today’s podcast is the medical management of uroliths. Struvites are a relatively common urolith encountered in dogs and cats, but for different reasons. Dogs more commonly develop struvite uroliths in response to a bacterial infection with Staphylococcus pseudointermedius or Proteus mirabilis. Not all stones are caused by infection, but the presence of any stone can predispose a patient to infection and secondary development of struvite formation. Antimicrobial therapy, thus, should be part of the medical management of urolith dissolution in the dog. Ideally, all uroliths from dogs should be cultured to guide medical management. In cats, it would be nice to culture these stones as well, but since most stones in cats are sterile, the cost to potential benefits should be weighed on a case by case basis. Urolith cultures do not always yield the same bacteria as the associated urine culture so, if you can, culture both! Antimicrobial therapy should be guided by these cultures. Based on the results from a positive urolith culture, the patient should undergo 7 days of directed antimicrobial therapy. If cultures are not available, but the stone is suspected to be one that is formed from presence of infection, the recommendation is to treat with 3-5 days of antimicrobial therapy. For non-urease producing infections such as with E.coli, the patient should only be treated with antimicrobials if they exhibit clinical signs attributed to a UTI. Otherwise, this falls under a subclinical bacterial infection and does not warrant treatment. If urease-producing bacteria are identified, they should always be treated based on culture results regardless of whether the patient is exhibiting symptoms of a UTI to prevent the formation of struvites. For stones that are not associated with infection, treatment of bacterial cystitis should continue for seven days. At any point during medical dissolution of uroliths, the stone is not dissolving as expected, a urine culture should be performed.
So there you have it, the latest 2019 guidelines for diagnosing and treating UTIs in cats and dogs. We recommend speaking with your local veterinary diagnostic lab to obtain surveillance data for your local area that will help guide empiric antimicrobial selections. Urinary tract infections should be treated for short duration of 3-5 days unless they are a recurring infection or a persistence of the same infection, in which case they should be treated for 7-14 days. Urine for culture submissions really need to make it to the lab and be processed onto culture media within 24 hours after collection or earlier if the sample is a voided sample. Pre-procedure cultures should be submitted to guide antimicrobial therapy prior to and after procedures. And urolith dissolution in dogs typically needs to be coupled with at least a short course of antimicrobial therapy unless supported otherwise by culture results, whereas cats should only receive antimicrobials if culture results are available and supportive for their use.
When in doubt, make sure you are aware of the newest updates in management and treatment of UTIs in dogs and cats based off these ISCAID guidelines!
UTI – Urinary tract infection
SDMA – serum symmetric dimethylarginine
DM – Diabetes Mellitus
IV – intravenous
International Society for Companion Animal Infectious Diseases (ISCAID) guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats . The Veterinary Journal 2019;247:8-25