Community-Acquired

Escherichia coli is by far the most frequent cause of uncomplicated community-acquired UTIs. At the molecular level, the E. coli, designated uropathogenic E. coli (UPEC), that causes UTIs is sufficiently different from other types of E. coli. Other bacteria frequently isolated from patients with UTIs are Klebsiella spp., other Enterobacteriaceae, Staphylococcus saprophyticus, and enterococci. In more complicated UTIs, particularly in recurrent infections, the relative frequency of infection caused by Proteus, Pseudomonas, Klebsiella, and Enterobacter spp. increases. In addition, community-acquired urinary tract infections are increasingly associated with multidrug-resistant organ isms such as extended β-lactamase-resistant E. coli.

Hospital-Acquired

The hospital environment plays an important role in determining the organisms involved in UTIs. Hospitalized patients are most likely to be infected by E. coli, Klebsiella spp., Proteus spp., staphylococci, other Enterobacteriaceae, Pseudomonas aeruginosa, enterococci, and Candida spp. The introduction of a foreign body into the urinary tract, especially one that remains in place for an extended period (e.g., Foley catheter), carries a substantial risk of infection, particularly if obstruction is present. Thirty five percent of all hospital-acquired infections are urinary tract infections. Eighty percent of those infections are associated with the use of an indwelling catheter. Consequently, UTI is the most common nosocomial infection in the United States, and the infected urinary tract is the most frequent source of bacteremia.

Miscellaneous

 Other less frequently isolated agents are other gram negative bacilli, such as Acinetobacter and Alcaligenes spp., other Pseudomonas spp., Citrobacter spp., Gardnerella vaginalis, Aerococcus urinae, and beta-hemolytic streptococci. Bacteria such as mycobacteria, Chlamydia trachomatis, Ureaplasma urealyticum, Campylobacter spp., Haemophilus influenzae, Leptospira, and certain Corynebacterium spp. (e.g., C. renale) are rarely recovered from urine. Because renal transplant recipients are immunosuppressed, these patients not only suffer from common uropathogens but are also susceptible to opportunistic infections with unusual pathogens. A study involving renal transplant recipients showed that for culture-negative urine, amplification of regions in bacterial 16S rRNA and subsequent analysis by high-performance liquid chromatography detected the presence of a number of known uropathogens as well as unusual agents. Salmonella spp. may be recovered during the early stages of typhoid fever; their presence should be immediately reported to the physician. If anaerobes are suspected, the physician should perform a percutaneous bladder tap unless urine can be obtained from the upper urinary tract by another means (e.g., from a nephrostomy tube). Communication by the clinician to the laboratory that such an agent is suspected is important for detecting such agents. In patients with “sterile pyuria,” Gram stain may reveal unusual organ isms with distinctive morphology (e.g., H. influenzae, anaerobes). The presence of any organisms on smear that do not grow in culture is an important clue to the cause of the infection. The laboratory can then take the action necessary to optimize chances for recovery.

In general, viruses and parasites are not usually considered urinary tract pathogens. Trichomonas vaginalis may occasionally be observed in urinary sediment, and Schistosoma haematobium can lodge in the urinary tract and release eggs into the urine. Adenoviruses types 11 and 21 have been implicated as causative agents in hemorrhagic cystitis in children.

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المزيد

مواضيع ذات صلة

Infections of the Urinary Tract : Pathogenesis

Infections of the Sinuses

Pathology of Acromegaly

clinical Features of Hyperprolactinaemia and Prolactinomas

Infections of the Ears : Diseases, Epidemiology, and Etiology of Disease

Encephalitis/Meningoencephalitis

Secondary Forms of Pure Red Cell Aplasia

Pathophysiology of Paroxysmal Nocturnal Hemoglobinuria

Clinical Manifestations of Paroxysmal Nocturnal Hemoglobinuria

Hypothyroidism: Etiology and Treatment

Introduction and History of Paroxysmal Nocturnal Hemoglobinuria

Diseases of The Central Nervous System