This patient presents with a urinary tract infection (UTI). The most common nitrite negative organism causing UTIs in sexually active women is Staphylococcus saprophyticus.
Urinary tract infections are infections affecting either the lower or upper urinary tract. S. saprophyticus is the second most common organism causing UTIs in sexually active women. Diagnostic markers for UTIs on urinalysis include positive Leukocyte esterase, which indicates a bacterial infection (presence of white blood cells), positive nitrates which indicate infection with gram negative bacteria (E. coli, etc.), and positive urease which indicates the presence of a urease producing organism such as Staph. Saprophysicus, Proteus and Klebsiella. Note that in infection with S. saprophyticus, nitrites would be negative as this is a gram positive organism.
Mehnert-Kay reviews the diagnosis and management of uncomplicated urinary tract infections. She states most uncomplicated urinary tract infections occur in women who are sexually active, with far fewer cases occurring in older women, those who are pregnant, and in men. E. coli is the leading cause of urinary tract infections, followed by S. saprophyticus. Trimethoprim-sulfamethoxazole has been the standard therapy for urinary tract infection; however, E. coli is becoming increasingly resistant to medications.
Simati et al. review dipstick urinalysis for the diagnosis of acute UTI. They review the pertinent findings and state dipstick urinalysis moderately improves the accuracy of clinical symptoms in establishing or excluding acute UTI in women. A positive nitrite test is more useful than a positive leukocyte esterase (LE) test, although both increase the odds of a UTI diagnosis. If nitrite and LE tests are negative, the odds of a UTI decrease by 40% - 60%.
Illustration A demonstrates the interpretation of a urinalysis. Illustration B reviews the risk factors for contracting a UTI.
Answer 1: K. pneumoniae is a urease producing organisms and thus would be expected to produce alkaline urine and have a urease positive test on urinalysis.
Answer 3: P. mirabilis is a urease producing organisms and thus would be expected to produce alkaline urine and have a urease positive test on urinalysis.
Answer 4: E. coli is the most common cause of UTIs, but would produce nitrite.
Answer 5: S. marcescens does cause UTIs, but is typically nosocomial and is not as common as E. coli, S. saprophyticus, or Klebsiella.
Mehnert-Kay SA. Diagnosis and management of uncomplicated urinary tract infections. Am Fam Physician. 2005 Aug 1;72(3):451-6. Review. PubMed PMID: 16100859.
PMID:16100859 (Link to Abstract)
Simati B, Kriegsman B, Safranek S. FPIN's clinical inquiries. Dipstick urinalysis for the diagnosis of acute UTI. Am Fam Physician. 2013 May 15;87(10):Online. PubMed PMID:
PMID:23939456 (Link to Abstract)