Question
A twenty five years old lady presented with frequency in passing urine and pain during micturition along with fever for the last five days. Microscopy of urine showed plenty of pus cells and bacilli . Answer the following:
- (a) What is your diagnosis . 1 mark(s)
- (b) Name of the common bacteria causing this condition . 2 mark(s)
- (c) What is significant bacteriuria . 1 mark(s)
- (d) How will you confirm the diagnosis in the laboratory. 4 mark(s)
- (e) What are the screening techniques for the presumptive diagnosis of significant 2 mark(s)
Answer
a) Diagnosis: Urinary tract infection (UTI) — likely acute cystitis with possible upper tract involvement, given frequency, dysuria, fever, and pyuria/bacilluria on microscopy.
b) Common causative bacteria Escherichia coli is by far the commonest cause (~80% of community-acquired UTIs, via uropathogenic strains with P-fimbriae). Other agents: Klebsiella pneumoniae, Proteus mirabilis (associated with urinary stones due to urease production), Enterococcus faecalis, Staphylococcus saprophyticus (particularly in young sexually active women), and Pseudomonas aeruginosa (typically catheter-associated/nosocomial UTI).
c) Significant bacteriuria Defined (Kass’s criterion) as the presence of ≥10⁵ colony-forming units (CFU) per mL of a single bacterial species in a properly collected, clean-catch midstream urine sample — this threshold distinguishes true infection from contamination by periurethral/perineal flora. Lower counts (e.g., ≥10²–10³ CFU/mL) may still be considered significant in symptomatic patients, in suprapubic aspirate samples, or with certain fastidious organisms.
d) Confirmation in the laboratory
- Urine culture on CLED (cystine-lactose-electrolyte-deficient) agar or MacConkey agar, using a calibrated (standard) loop to inoculate a known volume, allowing accurate colony counting; incubated aerobically at 37°C for 18–24 hours.
- Colony count interpreted against Kass’s criterion; organism identified by biochemical tests/automated identification, and antibiotic sensitivity testing performed on significant isolates.
- Proper specimen collection (clean-catch midstream sample, or catheter/suprapubic aspirate when indicated) and prompt transport/refrigeration (to prevent bacterial overgrowth giving falsely high counts) are essential for accurate interpretation.
e) Screening techniques for presumptive diagnosis
- Urine microscopy — pyuria (>5–10 pus cells/hpf in centrifuged sample) and bacilluria on Gram-stained uncentrifuged urine correlate well with significant bacteriuria.
- Dipstick tests — leukocyte esterase (detects pyuria) and nitrite test (detects nitrate-reducing organisms, mainly Enterobacteriaceae; less sensitive for non-nitrate-reducers like Enterococcus/Staphylococcus) provide a rapid bedside screen, though a negative result does not fully exclude UTI.