by Microbiologist Content
Urinary Tract Infection (UTI)
- An infection of the urinary tract is known as a urinary tract infection (UTI). The kidneys, ureters, urinary bladder, and urethra make up the urinary system.
- Although infections can develop everywhere throughout the urinary tract, from the kidney to the urethra, the majority of UTIs are only associated with bladder infections (cystitis).
- Bacteriuria is the term for the presence of bacteria in the urine. When the urine has 105 organisms or more per millilitre (108/1), it is typically considered significant.
- Cystitis is the medical term for bladder infection. Frequency, pain with urination (dysuria), suprapubic pain, occasionally hemoturia, and typically pyuria are all symptoms (increased number of pus cells in urine).
- When there is acute cystitis and pyuria but no germs are found in a normal culture, the condition is referred to as acute urethral syndrome (dysuria-pyuria).
- Pyelonephritis is the term used to describe kidney infection. It results in bacteremia, fever, rigours, pyuria, and loin discomfort.
- Uropathogenic organisms from the vaginal or gastrointestinal flora that colonise the periurethral mucosa are the primary cause of the majority of UTIs.
- Numerous methods allow organisms to ascend through the urethra and reach the bladder.
- With 150 million cases worldwide each year, urinary tract infections (UTIs) are among the most prevalent bacterial illnesses.
- As a result, they pose a serious threat to public health. A number of organisms are responsible for them, but Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus saprophyticus are the most frequent.
Table of Contents
- Types of UTI
- Causative Agents of UTI
- General Pathogenesis
- Symptoms of UTI
- Complications of UTI
- Risk Factors
- Diagnostic and Laboratory Findings
- Diagnostic Tests
- Treatment of UTI
- Prophylaxis and Prevention
Types of UTI
UTIs can be classified as simple or complex clinically.
Uncomplicated UTIs
These infections, known as lower UTIs (cystitis) and higher UTIs, generally afflict people who are otherwise healthy and have no anatomical or neurological abnormalities of the urinary system (pyelonephritis).
Rarely can simple cystitis develop into a serious infection.
Complicated UTIs
Complicated UTIs are defined as UTIs associated with factors that compromise the urinary tract or host defence, including urinary obstruction, urinary retention caused by neurological disease, immune-suppression, renal failure, renal transplantation, pregnancy and the presence of foreign bodies such as calculi, indwelling catheters or other drainage devices.
Causative Agents of UTI
- Both Gram-negative and Gram-positive bacteria, as well as certain fungi, are responsible for UTIs.
- Uropathogenic Escherichia coli is the most frequent culprit behind both simple and complex UTIs (UPEC).
- Klebsiella pneumoniae, Staphylococcus saprophyticus, Enterococcus faecalis, group B Streptococcus (GBS), Proteus mirabilis, Pseudomonas aeruginosa, Staphylococcus aureus, and Candida spp. follow UPEC in prevalence among the bacteria that cause simple UTIs.
- Following UPEC as the most frequent causative agent for complex UTIs, the most prevalent causative agents are Enterococcus, K. pneumoniae, Candida spp., S. aureus, P. mirabilis, P. aeruginosa, and GBS.
- In most cases, a single organism with a high concentration—typically 105 CFU/ml—causes UTIs.
- Patients with anatomical anomalies or foreign bodies may develop polymicrobial infections, however cultures that support the development of more than two distinct species should be suspect of colonisation or culture contamination.
General Pathogenesis
- Usually, the urethra is the route via which the germs that cause urinary tract infections enter the bladder. However, the lymphatic system or blood might potentially get infected.
- According to theory, the bacteria are often passed from the intestine to the urethra, with females being more susceptible because of their anatomical makeup.
- Most agents are able to bind to the bladder wall after entering the bladder and create a biofilm that inhibits the body's immune response, leading to an infection.
Symptoms of UTI
- Polyuria
- Hesitancy
- Incontinence
- Suprapubic pain
- Loin-to-groin pain e.g. flank and back
- Fever or chills
- Rigors
- Tachycardia
- Sepsis
Complications of UTI
- Renal failure can result from ongoing or repeated urinary tract infections (UTI).
- Acute or chronic kidney infection (pyelonephritis) brought on by an untreated UTI may result in permanent kidney damage.
- increased chance of preterm or low birth weight babies in pregnant mothers.
- Men with recurrent gonococcal urethritis have constriction of the urethra (urethral stricture).
- Sepsis is a potentially fatal infection-related consequence, particularly if the infection spreads to the kidneys through the urinary system.
Risk Factors
- Female gender, a past UTI, sexual activity, vaginal infection, obesity, and genetic predisposition are some of the risk factors linked to cystitis.
- Pregnancy
- abnormalities of the urinary system, such as anatomical blockage, an internal foreign object, recent surgery, or instrumentation.
- illnesses such diabetes, underlying renal disease, immunosuppression, a history of a difficult UTI, or a recent hospital stay.
- Women are more likely than males to have urinary tract infections because the female urethra is shorter. Additionally, both symptomatic and asymptomatic UTI are frequent during pregnancy.
- When there is urine retention because the bladder does not completely empty, or when urinary flow is restricted because of kidney stones, urinary schistosomiasis, an enlarged prostate (the most frequent cause of recurrent UTI in males), or a tumour, the risk of infection is raised.
Diagnostic and Laboratory Findings
- The common symptoms of an uncomplicated UTI can be used to make a reliable diagnosis.
- Patients may be treated empirically without the necessity for routine urine testing or urine culture.
- Patients should have an uninalysis and a urine culture if a complex UTI is suspected as well as if they exhibit pyelonephritis symptoms.
Diagnostic Tests
1. Urinalysis (dipstick or microscopic)
- When urine culture indicates growth >105 cfu/mL and the dipstick exhibits positive leukocyte esterase and nitrite responses, dipstick urinalysis performs best (sensitivity 84%; specificity 98%).
- Pyuria is a common symptom of UTI, and WBC casts indicate pyelonephritis (WBCs by microscopy or dipstick leukocyte esterase).
- Hematuria and proteinuria are additional common findings.
- It is normal for UTIs caused by E. coli and other Enterobacteriaceae to have a positive dipstick nitrite reaction, however this is not always the case for other uropathogens such Enterococcus.
2. Gram stain
- Unconcentrated urine Gram stain may be beneficial for detecting urine specimens that produce growth >105 cfu/mL, but it is unreliable for detecting specimens that produce lower level yet considerable growth.
- Gram staining is not advised for urine specimens due to the low sensitivity for spotting significant cultures and the labor-intensive procedure.
3. Routine culture
- One microliter of urine is inoculated onto SBA and selective (like MacConkey or CNA) agar to do quantitative culture.
- Therefore, 103 cfu/mL is the lower limit of detection.
- The quantity of growth, the type of specimen (clean catch versus invasively collected), the number of species isolated (pure culture versus mixed), the pathogenic potential of the isolate (typical uropathogen versus common contaminant), and the number of species isolated all affect how much workup (identification and susceptibility testing) is done.
Culture for possible complicated UTI
- A severe UTI may be predicted in symptomatic individuals at risk for complex UTI by bacteriuria at levels of 103–4 cfu/mL.
- For these individuals, culture techniques using a 10-microliter inoculum enable growth to be detected at a lower detection limit of 102 cfu/mL.
- When one or two uropathogens are isolated in levels >103 cfu/mL (as opposed to the 104 cfu/mL criterion used for regular cultures), thorough ID and appropriate susceptibility tests are undertaken. Otherwise, the scope of workup follows similar criteria used for routine cultures.
Note:
Patients with renal or perinephric abscess may have normal urine cultures if the affected tissue is not in contact with the collecting system. Such localised infections are drained for therapeutic purposes as well as to gather samples for Gram staining, culture, and other laboratory tests.
4. Other Laboratory Testing
- Women who arrive with otherwise simple UTIs may benefit from pregnancy testing.
- Blood cultures are advised for individuals with fever, hypotension, or other sepsis-related symptoms who have complex UTI.
- It is advised to do further laboratory tests appropriate for the clinical presentation.
Treatment of UTI
Antibiotics are the mainstay of the therapy.
However, because the antibiotics do not remain in the urethra long enough to be effective, they are ineffective for treating urethral syndrome.
Increasing fluid intake will help wash germs out of the urethra during treatment.
UTI (Uncomplicated and Complicated)
- 1st line: PO Trimethoprim
- 2nd line (if 1st line contradicted) : PO Nitrofurantoin
- Pregnancy: PO Cephalexin
Pyelonephritis
- 1st line: IV Co-amoxidav + IV Gentamicin
- 2nd line (if 1st line contradicted) : PO or IV Ciprofloxacin + IV Gentamicin
- Pregnancy: IV Cefuroxime
- Complicated UTIs are more difficult to treat and usually requires more aggressive evaluation, treatment and follow-up.
- It may require identifying and addressing the underlying complication.
- Increasing antibiotic resistance is causing concern about the future of treating those with complicated and recurrent UTI.
Prophylaxis and Prevention
- Prophylactic antibiotics are used in children who experience recurrent UTIs in order to try and preserve renal function.
- Drinking plenty of fluids especially water.
