Urinary tract infections

Learning Objectives At the end of this lecture, the student should be able to: list the main microorganisms responsible from UTI explain the importance of significant bacteriuria and quantitative culture method List the main advantages and disadvantages of each type ofsample for the laboratory diagnosis List the laboratory tests for UTI

Urinary tract infections Urinary tract infections are common, especially among women 20-30% of women have recurrent urinary tract infections (UTI) at some time in their life. UTIs in men are less common and primarily occur after 50 years of age.

Urinary tract infections Although the majority of infections are acute short-lived they contribute to a significant amount of morbidity in the population.

Urinary tract infections Severe infections result in a loss of renal function and serious long-term sequelae. In females, a distinction is made between cystitis, urethritis and vaginitis, but the genitourinary tract is a continuum and the symptoms often overlap.

Normal urethral flora Coagulase negative staphylococci Viridans nonhemolytic streptococci Lactobacilli ♀ Diphtheroids Non pathogenic Neisseria species Commensal Mycobacterium species Yeasts

ACQUISITION AND ETIOLOGY Bacterial infection : usually acquired by the ascending route from the urethra to the bladder The infection may then proceed to the kidney. Occasionally, bacteria infecting the urinary tract invade the bloodstream to cause septicemia.

ACQUISITION AND ETIOLOGY Bacterial infection : Less commonly, infection may result from hematogenous spread of an organism to the kidney with the renal tissue being the first part of the tract to be infected.

ACQUISITION AND ETIOLOGY From an epidemiological viewpoint, UTIs occur in two general settings: 1-community-acquired and 2-hospital (nosocomially) acquired, most often being associated with catheterization. Hospital-acquired UTIs, while less common than community acquired, contribute significantly to overall nosocomial infection rates.

Bacterial UTI The Gram-negative rods: Escherichia coli (the commonest cause of ascending UTI ) Other members of the Enterobacteriaceae: -Proteus mirabilis -Klebsiella, Enterobacter, Serratia spp. and Pseudomonas aeruginosa

Bacterial UTI The Gram-negative rods: Enterobacteriaceae: -Proteus mirabilis: associated with urinary stones (calculi), probably because this organism produces a potent urease, which acts on urea to produce ammonia, rendering the urine alkaline.

Bacterial UTI The Gram-negative rods: Enterobacteriaceae: -Klebsiella, Enterobacter, Serratia spp. and Pseudomonas aeruginosa : are more frequently found in hospital- acquired UTI because their resistance to antibiotics favors their selection in hospital patients

Bacterial UTI Gram-positive species Staphylococcus saprophyticus : especially in young sexually active women. Staphylococcus epidermidis and Enterococcus species are more often associated with UTI in hospitalized patients (especially those with AIDS), where multiple antibiotic resistance can cause treatment difficulties.

Bacterial UTI Gram-positive species corynebacteria and lactobacilli Obligate anaerobes: very rarely

Bacterial UTI Hematogenous spread to the urinary tract: other species may be found: Salmonella typhi, Staphylococcus aureus Mycobacterium tuberculosis (renal tuberculosis).

Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier

Viral UTI rare hemorrhagic cystitis and other renal syndromes

Certain viruses may be recovered from the urine in the absence of urinary tract The human polyomaviruses, JC and BK cytomegalovirus (CMV) and rubella

Viral UTI Adenovirus:hemorrhagic cystitis The rodent-borne hantavirus mumps and HIV

Other causes of UTI Candida spp. and Histoplasma capsulatum The protozoan: Trichomonas vaginalis Schistosoma haematobium : hematuria.

PATHOGENESIS A variety of mechanical factors predispose to UTI Pregnancy, prostatic hypertrophy, renal calculi, tumors and strictures are the main causes of obstruction to complete bladder emptying Catheterization is a major predisposing factor for UTI A variety of virulence factors are present in the causative organisms The healthy urinary tract is resistant to bacterial colonization

LABORATORY DIAGNOSIS A key feature is the detection of significant bacteriuria. Infection can be distinguished from contamination by quantitative culture methods

In health the urinary tract is sterile, the distal region of the urethra is colonized with commensal organisms, which may include periurethral and fecal organisms. As urine specimens are usually collected by voiding a specimen into a sterile container, they become contaminated with the periurethral flora during collection. Infection can be distinguished from contamination by quantitative culture methods.

In health the urinary tract is sterile, the distal region of the urethra is colonized with commensal organisms, which may include periurethral and fecal organisms. As urine specimens are usually collected by voiding a specimen into a sterile container, they become contaminated with the periurethral flora during collection. Midstream urine (MSU) Infection can be distinguished from contamination by quantitative culture methods.

Bacteriuria is defined as 'significant' when a properly collected midstream urine (MSU) specimen is shown to contain over 105 organisms/ml. Infected urine usually contains only a single bacterial species. Contaminated urine usually has <104 organisms/ml and often contains more than one bacterial species Distinguishing infection from contamination when counts are 104-105 organisms/ml can be difficult.

Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier

'significant bacteriuria' urine specimens collected from: Catheters nephrostomy tubes suprapubic aspiration directly from the bladder: any number of organisms may be significant because the specimen is not contaminated by periurethral flora.

'significant bacteriuria' Infection of sites in the urinary tract below the bladder by organisms that are not members of the normal fecal flora: may not lead to the presence of significant numbers in the urine.

Urine samples from babies and young children Difficult 'Bag urine' may be collected by sticking a plastic bag to the perineum in girls or to the penis in boys such specimens are frequently heavily contaminated with fecal organisms.

Transport of urine specimens with minimum delay because urine is a good growth medium for many bacteria and multiplication of organisms in the specimen between collection and culture will distort the results

Ideally, samples should be collected before antimicrobial therapy is started. If the patient is receiving, or has received, therapy within the previous 48 h, this should be stated clearly on the request form.

For patients with a catheter a catheter specimen of urine is used Patients should not be catheterized simply to obtain a urine sample.

Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier

Special urine samples M. tuberculosis Schistosoma haematobium

Special urine samples M. tuberculosis three early morning urine samples on consecutive days

Special urine samples S. haematobium the last few ml of a late morning urine sample collected after exercise

Laboratory investigations Microscopic examination of urine allows a rapid preliminary report Bacteria may be seen on microscopy when present in the specimen in large numbers. However, they are not necessarily indicative of infection, but may indicate that the specimen has been poorly collected or left at room temperature for a prolonged period of time.

Laboratory investigations Microscopic examination of urine The presence of red and white blood cells, although abnormal, is not necessarily indicative of UTI.

The presence of red cells Hematuria infection of the urinary tract and elsewhere (e.g. bacterial endocarditis) renal trauma calculi urinary tract carcinomas clotting disorders thrombocytopenia Occasionally, red blood cells may contaminate urine specimens of menstruating women.

The presence of white cells pyuria White blood cells are present in the urine in very small numbers (e.g. <10/ml) in health a count of over 10/ml is considered abnormal, but is not always associated with bacteriuria.

Microscopic examination of urine Sterile pyuria is an important finding and may reflect: concurrent antibiotic therapy other diseases such as neoplasms or urinary calculi infection with organisms not detected by routine urine culture methods. Renal tubular cells, seen in the urine of aspirin-misusers, may be confused with white blood cells. Urinary casts are also indicative of renal tubular damage.

A laboratory diagnosis of significant bacteriuria requires quantification of the bacteria Conventional culture methods produce results within 18-24 h, but rapid methods (e.g. based on bioluminescence, turbidimetry, leukocyte esterase/nitrate reductase test, etc.) are also available.

storage - the urine must be cultured within 1 h of collection or held at 4°C for not more than 18 h before culture antibiotic treatment - in a patient receiving antibiotics, smaller numbers of organisms may be significant and may represent an emerging resistant population; simple laboratory methods are available to detect antibacterial substances

fluid intake - the patient may be taking more or less fluid than usual, and this will clearly influence the quantitative result the specimen - the quantitative guidelines are valid for MSU specimens; they do not apply to catheter specimens, suprapubic aspirates or nephrostomy samples.

Laboratory diagnosis 1. Microscopy 2. Quantitative culture 3. Susceptibility testing

Infection criteria Gram staining→ presence of leukocytes and microorganisms

Bacteriuria: microscopic examination: Presence of significant number of bacteria in uncentrifuged urine sample–high magnifaction power in immersion field; x1000- with Gram stain): ≥ 1 bacterium or bacteria/high power field. conventionally accepted to correspond ≥105 CFU/mL)

Bacteriuria: Culture: Presence of significant number of bacteria inuncentrifuged urine sample (quantitative culture result): ≥ 103 to ≥105 CFU/mL

Culture results Bacteria/ no.of coloni In asemptomatic patients 105 cfu/ml (male 104): identification and antibiotic susceptibility test (AST) 104- 105 cfu/ml : contact with clinician if >2 bacteria is seen 102 cfu/ml : significant if it is taken from catheter 10 cfu/ml: significant if its suprapubic aspiration

Downloaded from: StudentConsult (on 28 February 2011 02:58 PM) © 2005 Elsevier

Pathogens E. coli (%50-90) Other Enterobacteriaceae S. saphrophyticus (♀) P. aeruginosa Enterococcus spp. Other CNS