Recommendations regarding urinary tract infections have gone through significant changes as our understanding of this disease and the concerns about multi-drug resistant infections have grown. Improper therapy can not only lead to health concerns in your patient and wasted money for your client, but also increase the amount of multi-drug resistant bacteria that are present on that patient and within the community as a whole, which puts all of us at risk. Therefore, it is incredibly important that we balance out the various factors as we decide what truly is in the best interest of our patients. If you asked me 10 years ago, I would have told you to check periodic urine cultures on all immunosuppressed patients due to the risk of development of pyelonephritis if an infection was left untreated. After attending an ACVIM Forum Lecture “Decision Making in Urinary Tract Infections and Bacteruria” by Scott Weese in 2015 ( https://www.vin.com/members/cms/project/defaultadv1.aspx?id=6790386&pid=11719&), my approach to this urinary tract infections, in general, has dramatically changed. In 2011, Weese et al published “Antimicrobial Use Guidelines for Treatment of Urinary Tract Disease in Dogs and Cats: Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases” which is available at www.iscaid.org. This consensus statement provides a fabulous reference to help clinicians direct therapy and is a “go-to” reference for urinary tract infections.
Subclinical Urinary Tract Infections:
It is important to recognize when bacteria in the urinary system needs to be treated and when it needs to be ignored. We once considered any bacteria in the urinary system as a problem but more recently, we recognize that there are pathogenic and non-pathogenic bacteria in the urine. We only need to be treating pathogenic bacteria. The non-pathogenic bacteria should be left alone as they may be keeping pathogenic strains at bay. The first question to ask yourself is: Are the bacteria causing this patient any issues? Think about the following. Is the patient showing lower urinary tract signs such as hematuria, pollakiuria, stranguria, urinary accidents or licking his penis or her vulva? Does the patient have signs of pyelonephritis such as sudden increase in renal values or ultrasound changes suggestive of pyelonephritis? Is the patient’s diabetes or Cushing’s disease acutely unregulated? Any of these could be symptoms that bacteria in the urine is causing the patient issues. If the patient is not having any clear issues related to the bacteria in the urine, do not treat the patient for a urinary tract infection. For example, a patient comes in for a wellness examination and is doing great at home. You submit a CBC, chemistry and urinalysis as part of a wellness panel. You see bacteria in the urine. The first question that you should ask yourself is: did the family mention any symptoms that could be related to a urinary tract infection. If the answer is no, when you call the family with the results, ask specific questions to make sure that the family has not forgotten to report symptoms at home. If, after questioning the family, there are no signs that the bacteria is causing issues, ignore the bacteria for now and instead just review symptoms for the family to watch for and tell them to contact you if there are any concerns. If there are concerns from the history, physical examination, or other lab work that the infection may be clinically relevant, have the patient come back for a urine culture.
Clinically significant urinary tract infections can be broken down into Simple Uncomplicated and Complicated urinary tract infections. For either type of infection, ideally, you should get a urine culture to help guide your therapy. Clients may resist performing a urinary culture due to the up-front costs. If this situation occurs, you should remind clients that inappropriate antibiotics can waste money and time and may ultimately cost families significantly more than they will spend with a urine culture to direct therapy. In addition, clients who do not want to perform a urine culture should be reminded of the growing multi-drug resistance problems and that giving the family pet inappropriate antibiotics may lead to more multi-drug resistant bacteria in their house and on their family, increasing the risk to all family members.
Simple Uncomplicated Urinary Tract Infections:
Simple urinary tract infections are just that, straightforward infections without complicating factors. These patients are otherwise healthy and do not have any anatomical issues in their urinary tracts. If the patient has either of these issues or if he or she has had 3 or more urinary tract infections within a 12 month period, the patient is no longer classified in this category. A urinalysis and culture are recommended for these patients. As is often the case, if the patient’s symptoms are significant, antibiotics can be started while awaiting the results of the culture. In general, for urinary tract infections, the “smallest gun” antibiotic that will treat the infection should be used. The consensus statement recommends starting these patients on either amoxicillin 11-15 mg/kg PO q8 or trimethoprim-sulfa 15 mg/kg PO q 12. Once the results of the culture return, if the current antibiotics are listed as resistant and the patient has not shown any clinical improvement, therapy should be altered based on the culture results. Due to the fact that the kidneys super-concentrate certain antibiotics in the urine, some patients will have a clinical response to an antibiotic that is listed as resistant on the culture panel. In these patients, it is reasonable to continue the therapy that appears to help and then obtain a culture 5-7 days after the therapy has ended to verify that the infection has truly been cleared. The length of time these patients should be treated is controversial. Traditionally, the recommendation has been 7-14 days. The Working Group for the consensus statement feels that less than 7 days may be effective and, therefore, their recommendation is 7 days for these patients. In 2012, Westropp et al ( https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1939-1676.2012.00914.x ) showed that high dose enrofloxacin (18-20 mg/kg) q 24 hours for 3 days had cure rates similar to that of 14 days of Clavamox. This shorter treatment time may help improve owner compliance and, therefore, increase the overall cure rate and decrease the risk of building multi-drug resistant infections. In simple, uncomplicated urinary tract infections, post-treatment urinalysis or urine cultures are not warranted. Instead, families and clinicians should focus on symptoms to determine if the infection has been cleared. Remember, if there are documented bacteria without symptoms, the recommendation is to not start treatment so these post-treatment assessments should be reserved for patients who continue to be symptomatic after therapy.
Complicated Urinary Tract Infections:
Complicated urinary tract infections are defined as occurring in patients with anatomical or functional abnormalities (uroliths, poor sphincter tone, bladder masses), patients with comorbidities that make it more difficult to clear infections (diabetes, Cushing’s, hypothyroidism, or on immunosuppressive medications), patients with persistent infections, or patients with recurrent infections. Recurrent urinary tract infections are defined as 3 or more UTIs within a 12 month period. Recurrent infections can be classified as reinfections (a different type of bacterial infection occurring within a 6 month period after successful treatment of a UTI) or relapse (the same type of bacterial infection occurring within a 6 month period after successful treatment of a UTI). To truly define an infection as a relapse, genotyping should be performed, something that is not typically pursued in veterinary medicine. A refractory infection is defined as an infection in which you continue to get positive culture results despite seemingly appropriate antibiotics.
If a complicated urinary tract infection is diagnosed, a culture is highly recommended. If the patient’s symptoms dictate starting empirical therapy pending the results of the culture, amoxicillin or trimethoprim-sulfa are good choices. While treating the infection, the clinician should try to address the underlying factor(s) that made the infection complicated. For example, remove uroliths (remembering to culture the bladder wall) or work on better regulating diabetes, Cushing’s disease or hypothyroidism. Typically, 4 weeks of antibiotics is recommended for these patients. Post-treatment cultures should be considered 5-7 days after stopping antibiotics in patients with recurrent or refractory infections.
Urine cultures should always be performed in these patients. In most patients, cystocentesis cultures are adequate. In some patients, pyelocentesis cultures are needed to obtain a definitive diagnosis. While awaiting the results of the urine culture, the most highly recommended empirical therapy is fluoroquinolones. You will notice at Hope that we will sometimes use Unasyn instead of, or in addition to, fluoroquinolones if the differentials for the acute renal failure include both pyelonephritis and Leptospirosis since fluoroquinolones will not treat Lepto. Treatment should last 4-6 weeks. A urine culture is recommended 1 week into therapy; if the therapy is working appropriately, there should be no growth of bacteria on this culture. A urine culture is also recommended 1 week after therapy is finished to verify that the bacterial infection has been resolved.
The antibiotic should not be given to patients with urinary catheters for the sole purpose of preventing infections. Previously, it was recommended to culture the tip of the catheter when the catheter was removed but Smarick, et al, 2004 ( https://avmajournals.avma.org/doi/abs/10.2460/javma.2004.224.1936 ) showed that these results were not predictive of the development of a UTI. There is also no evidence for performing post-catheter-removal cystocentesis cultures in the basic urinary catheter case but it is reasonable to perform cultures in the high-risk patients or in patients in which infections could lead to significant issues (blocked male cats with a high risk of reblocking).
Patients with urinary catheters in place can develop urinary tract infections. In these patients, a urine culture is highly recommended. If it is possible for the patient to go without the urinary catheter, remove the catheter and obtain a cystocentesis culture after allowing the bladder to refill. If the integrity of the bladder is such that a cystocentesis cannot be safely obtained, you can obtain the culture through the catheter prior to removal but this technique is significantly less ideal. If the patient still needs to have a urinary catheter, the catheter should be replaced with a new one and a culture should be obtained through the newly placed catheter. Several ml of urine should be removed prior to taking the culture to try to obtain the most accurate culture possible.
By following the above recommendations, we can hopefully effectively treat our patients’ infections while limiting the spread of multi-drug resistant infections as much as possible.
Submitted by Laurie Prober VMD, DACVIM