The phrase urinary tract infection is a broad term used to describe both bacterial colonization of the urine and invasion of structures in any part of the urinary tract. Colonization of the urine, that is, multiplication of large numbers of bacteria in the urine, is often difficult to distinguish from actual tissue invasion eliciting a host response, because of the frequent tendency of urinary tract infections to exhibit either few or no symptoms. This phenomenon is known as asymptomatic bacteriuria At any given point in time, an individual may have bacteriuria alone, or bacteriuria with silent tissue invasion, or bacteriuria accompanied by signs of inflammation of the bladder (cystitis) or kidneys (pyelonephritis).
Infections of the structures of the urinary tract are usually accompanied by colonization of the urine which bathes the kidney, ureter, bladder, and urethra. Thus, bacteriuria is the most common denominator of urinary tract infections. Bacteriuria may be absent, however, when the infected focus is not contiguous with the urine as in early lesions of hematogenous pyelonephritis, when there is marked obstruction of the affected portion of the tract or when it is masked by antimicrobial.
The species of bacteria most likely to be recovered in individuals with bacteriuria depends, for the most part, upon previous history of infection, receipt of antimicrobial therapy, hospitalization, and instrumentation of the urinary tract. In this respect, the bacterial flora found in individuals with asymptomatic bacteriuria is no different from that in cases of clinically obvious pyelonephritis.
Entero- bacteriaceae are by far the most common organisms identified. E. coli generally accounts for more than 80 per cent of all species recovered in so-called uncomplicated cases, whereas Proteus, Klebsiella, Enterobacter, Pseudomonas aeruginosa, enterococci, and Staphylococcus aureus are more likely to be found in patients who have had previous infection or instrumentation (the so- called complicated group).
Occasionally, organisms such as Serratia marcescens, Mima-Herellea, Candida albicans, and even Cryptococcus neo- formans may be significant and produce disease in diabetics and in patients treated with corticosteroids and immunosuppressive agents. Diphtheroids, Staphylococcus epidermidis, and micro- aerophilic streptococci are highly suspect as contaminants. They usually will not be isolated on repeated culture. They should not, however, be dismissed if repeatedly recovered under optimal conditions of collection.Despite the abundance of anaerobic flora in the gut, they are actually rare in urinary infections, presumably owing to the poor growth of these organisms in urine.
Microscopic Diagnostic Methods.
Rapid diagnostic methods are available by either preparation of a Gram stain of unsedimented urine and examination with an oil immersion lens, or by study of the centrifuged urinary sediment for bacteria, employing the high dry objective under reduced light with or without the addition of methylene blue. The Gram stain has been the most widely used of these methods and correlates about 80 to 90 per cent with quantitative culture. Examination of the unstained sediment as prepared for search for formed elements in the urine is very helpful. It is much less time consuming than preparation of a stained slide, and can be done in cpnjunction with the routine examination for formed elements.
This method lends itself particularly well in office practice to assessing the presence of a urinary tract infection. The criterion for a positive sediment is the presence of many (preferably more than 20) obvious bacteria. The presence of marked pyuria can mask bacteria in the sediment. Fresh urine is required, because crystals will also obscure the bacteria. If crystals do form, the urine should be warmed until they dissolve.
Ten or more leukocytes per high-powered field in the centrifuged specimen is usually accepted as representing pyuria. When inflammation of the bladder mucosa is intense, there ma;. be saw erythrocytes in the urine, and gross he sometimes occurs. .
Epidemiology of Urinary Tract Infection
Extend epidemiologic studies have provided informalic® of the frequency of bacteriuria in various populations. Bacteriuria in the newborn period has bee’ difficult to define because of problems inherent in collection, but information is being obtained with the widespread use of the bladder puncture method. Infection of the urinary tract in this age group appears to be part of a generalized, life-threatening gram-negative sepsis, and is more common in boys than girls. Symptomatic urinary infections, particularly among girls, are prominent in the preschool years, and are frequently associated with important obstructive or neurogenic lesions.
Urologic investigation is extremely valuable in this age group. It is mandatory in males of any age because of the high frequency of important structural abnormalities found (valves, malformations, obstructive and neurogenic lesions). The prevalence of bacteriuria among schoolgirls is 1.2 per cent; it is only 0.03 per cent in boys of the same’ age. The incidence rate in girls is 0.3 per cent per year; it is linear with time throughout the school years and is unaffected by menarche. The cumulative frequency or urinary infection in girls occurring at one time or another during the school years exceeds 5 per cent.
Why Urinary infection Is Common In Marriage
Bacteriuria in schoolgirls is independent of socioeconomic status and race, and is not increased in diabetic girls. The prevalence of bacteriuria rises with age and is increased in lower socioeconomic groups, probably because of limited antimicrobial therapy delivered to this population. Urinary infection is common after marriage. The “honeymoon cystitis” syndrome may be due to either infection or local irritation, and these should be clearly differentiated by culture. Bacteriuria in pregnancy varies from 2 to 6 per cent, depending upon age, parity, and socioeconomic groups. Early detection and treatment of bacteriuria in this age group will prevent the emergence of symptomatic infection. Elderly women may have frequencies of bacteriuria as high as 10 per cent; this rate may rise even higher in hospitalized patients, particularly diabetics. Bacteriuria in the male begins to appear in the “prostate” years, and is often initiated by instrumentation.
Role of Instrumentation.
Persistent bacteriuria follows single catheterizations at a frequency of 1 to 2 per cent and with open indwelling catheter drainage exceeds 90 per cent within three to four days. This may lead to life-threatening pyelonephritis and gram-negative sepsis. Fortunately, it is partially avoidable by (1) careful preselection of criteria for catheterization, and (2) use of aseptic closed drainage or antimicrobial bladder rinse during prolonged catheterization. The catheter should be removed as soon as it is no longer needed.