ASB is defined as the presence of bacteria in the urine in quantities of 10⁵ colony-forming units per millilitre (cfu/mL) or more in two consecutive urine specimens in women or one urine specimen in men, in the absence of clinical signs or symptoms suggestive of a UTI [8]. It is more common in diabetic older patients, while it is constant in indwelling catheter holders and very frequent in incontinent women. The prevalence of ASB is estimated to be between 6 and 10% in women older than 60 years and approximately 5% in men older than 65 [9]. In institutionalised adults the incidence of bacteriuria is even higher, with estimates ranging from 25 to 50% for women and 15 to 35% for men. Table 16.3 shows the prevalence of bacteriuria in different countries and ages. Although ASB increases the risk of symptomatic UTI, it should not be treated except in those patients undergoing invasive genitourinary procedures [3].

A common clinical scenario is an older patient, maybe living in a residential home, who is referred to the ED with a history of increasing confusion, being unable to provide clear associated symptoms. The patient could have dark and offensive smelling urine; the dipstick test is positive for leucocyte esterase and nitrites. A urine culture is sent (and will be positive), UTI is diagnosed, and antibiotic treatment is started. However, fever or other indices of systemic inflammation (hypothermia, CRP, raised white cell count) or genitourinary tract infection are lacking; other sources of infection (pneumonia, diverticulitis, endocarditis, etc.) have not been ruled out; and alternative diagnoses of acute confusion have not been adequately taken into account. For example, the patient could have recently started codeine for knee pain, and this could be the cause of increasing confusion, constipation, reduced fluid intake with consequent dehydration, and change in the character of urine that is chronically bacteriuric. An apparently simple and well-managed clinical case becomes a misdiagnosis and a missed diagnosis of the true cause of delirium [4]. Moreover, unnecessary antibiotic treatment may frequently cause harm (rash, drug interactions, development of antibiotic resistance, and disruption of intestinal microbiome) [11].

In older patients the symptoms and signs of UTI may be atypical and difficult to distinguish from other urinary diseases. Older adults with UTI are more likely to present to the ED with altered mental status rather than fever or classic urinary symptoms; however, when present, acute dysuria is more specific for UTI than urinary frequency or urgency [6]. Atypical presentations also abound in older patients with pyelonephritis, but fever and chills are more consistently present [6]. Another important symptom of UTI could be the pain in the suprapubic area, the flank, or the back, which in the non-cooperative patient could be suggested by agitation, irritability, and increased confusion (delirium) with increased incidence of falls. Even if incontinence could be a risk factor for UTI, it may also represent a symptom of the disease. When UTI evolves into sepsis or septic shock, typical symptoms—like hypotension, tachycardia, tachypnoea, anorexia, respiratory distress, and abdominal tenderness—may occur but can be delayed or onset abrupt.

As mentioned above, the simple evidence of cloudy or malodorous urine is not sufficient to start an antimicrobial treatment, as it could be due to epithelial cells or mucus, dehydration, or poor hygiene, while the evidence of haematuria could be due to different causes, such as cancer or medication. In older patients also fever may be absent or late in onset, or they could be hypothermic with sepsis. When present, fever is the most important sign, but it is important to exclude other sources of infection.

Multidrug-resistant organisms (MDROs) are increasing over time, due to the widespread and frequently inappropriate use of antibiotics for UTI [14]. Although MDROs are more common in healthcare settings, the prevalence of resistant urinary pathogens in community populations is also growing [5]. Figure 16.1 shows the antimicrobial resistance in E. coli-positive urinary cultures in a North Italian environment, with a high prevalence of older people [5]. These data suggest that it is important to know the epidemiology and antibiotic sensibility in each environment, setting, and geographical location, to be able to conduct a correct education of doctors to use antibiotics that are effective and that are not increasing resistances, which vary widely among Europe.