Laboratory Diagnosis of Urinary Tract Infections in Adult Patients

Sir—Several points regarding the laboratory diagnosis of urinary tract infection (UTI) deserve clarification to supplement the timely article by Wilson and Gaido [1]. First, it is imperative that physicians appreciate the distinction between microbiologically versus clinically significant bacteriuria. Although interpretive criteria based on specimen type, colony count, and number of organisms, such as the criteria shown in table 4 of the article by Wilson and Gaido [1], can be used to assess the likelihood that a positive urine culture result represents contamination instead of true bacteriuria, the mere presence of true (i.e., microbiologically significant) bacteriuria provides no information whatsoever regarding whether treatment is needed. This is a clinical judgment that is based on the recognition that, for adults, antimicrobial therapy for UTI should be reserved almost exclusively for treating symptomatic infections. Asymptomatic bacteriuria is usually clinically insignificant and should be treated only in pregnant women and before invasive urologic procedures, regardless of the bacterial colony count, organism, and degree of associated pyuria. Second, several studies have shown that, in young women with acute dysuria, so-called low-count bacteriuria is usually both microbiologically and clinically significant and is substantially prevalent, such that a concentration criterion of ⩾105 cfu/mL (or even ⩾104 cfu/mL) for clinical significance is highly insensitive. Use of the term “urethral syndrome” to describe the disorder present in dysuric women with low-count coliform bacteriuria may be more misleading than helpful, because most of these patients actually have straightforward Escherichia coli UTI that will respond to standard single-dose or 3-day treatment with an appropriate agent. Third, among chronically catheterized patients, high-count (and often polymicrobial) bacteriuria is almost universally prevalent. Although these organisms might be considered to be contaminants in the sense that they are contaminating the catheter system, they represent true bacteriuria and cannot be dismissed as microbiologically or clinically irrelevant if the patient has symptoms possibly attributable to UTI. Thus, when clinical suspicion for symptomatic UTI is high in such patients, physicians must ask the laboratory to evaluate the multiple organisms involved to facilitate effective antimicrobial therapy, particularly because the specific organisms that are present, as well as the associated antibiograms, are highly unpredictable in these cases. Conflict of interest.