• Urinary tract infection is the second most common infection after respiratory tract infection.
  • Urinary tract infection (UTI) is defined as a disease caused by microbial invasion of the genitourinary tract that extends from the renal cortex of the kidney to the urethral meatus. 
  • The presence of detectable bacteria in the urine is named as bacteriuria.
  • Presence of pus cells in urine denotes pyuria which most often accompanies UTI.

Types of UTI:-

  • It is divided into two broad categories: 
  1. Lower UTI
  2. Upper UTI

1)LOWER UTI

(1) Urethritis

(2) Cystitis

(3) Prostatitis

Urethritis

  • Urethritis is a condition in which the urethra, or the tube that carries urine from the bladder to outside the body, becomes inflamed and irritated.

Cystitis

  • Cystitis is inflammation of the bladder, usually caused by a bladder infection.

Prostatitis

  • Prostatitis is swelling and inflammation of the prostate gland, a walnut-sized gland situated directly below the bladder in men.

2) Upper UTI

i) Acute pyelitis

(ii) Acute pyelonephritis

i) Acute pyelitis

  • Infection of pelvis of kidney.

(ii) Acute pyelonephritis

  • Infection of parenchyma of kidney.

Predisposing Factors

1. Gender

  • Females are more frequently affected by UTI due to the following reasons:

(a) Short length of urethra.

(b) Sexual intercourse leads to introduction of bacteria into the bladder.

2. Pregnancy–

3. Obstruction to flow of urine.

4. Neurogenic bladder dysfunction. 

Clinical Features

  • Symptoms include frequency, dysuria, supra pubic pain along with loin pain. There may be fever with rigors. 
  • UTI is more frequent in women than men. 

Causative Organisms

A. Gram Negative Bacilli 

1. Escherichia coli

2. Klebsiella spp.

3. Proteus spp.

4. Enterobacter

5. Pseudomonas aeruginosa

6. Serratia

B. Gram Positive Cocci 

1. Enterococci e.g. E. faecalis 

2. Staph. saprophyticus 

3. Staph. aureus 

C. Miscellaneous

1. Mycoacterium tuberculosis

2. Citrobacter

3. Salmonellae

4. Str. pyogenes

5. Str. agalactiae

6. Gardnerellavaginalis

D. Fungus

  • Candida albicans may cause UTI in diabetes and immunocompromised patients.

Laboratory Diagnosis

SAMPLE COLLECTION

1. Midstream Urine Specimen (MSU)

2. Catheter Specimen

Transport

  • As urine is a good culture medium, specimens after collection should reach the laboratory with minimum delay, if this is not possible; the specimen is to be refrigerated at 4°C.

Laboratory Methods

  • Part of the specimen is used for bacteriological culture and the rest is examined immediately under the microscope.

1. Microscopy


 Urine is centrifuged and deposit is examined under microscope for detecting pus cells, epithelial cells, erythrocytes and bacteria. 

2. Culture

  1. Uncentrifuged urine is inoculated on blood agar and MacConkey’s agar. 
  2. Culture plates are incubated at 37°C for 24 hours. 
  3. Most laboratories use a semi quantitative method (standard loop technique) for culture of urine specimens.

3. Standard Loop Technique

  • A standard calibrated loop is used to culture a fixed volume of un-centrifuged urine. 
  • Blood agar and MacConkey’s agar are used and incubated at 37°C for 24 hours, next day, the number of colonies obtained is counted and the total count per ml is calculated.

Interpretation of results

  • Kass (1956) gave a criterion of active bacterial infection of urinary tract as follows:

(i) Count more than 105 bacteria of single species per ml: Significant bacteriuria which indicates active UTI.

(ii) Between 104 to 105 bacteria per ml is of doubtful significance, specimen should be repeated for culture.

(iii) Less than 104 bacteria per ml : no significant growth but regarded as contaminant. 

Contamination is also considered when three or more bacteria are isolated.