UTI: Pathogenesis and Etiology with Case

00:01 Hello and welcome back to the Nephrology curriculum.

00:04 Today we're going to be talking about urinary tract infection or UTI.

00:09 Let's start out with a clinical case.

00:11 The 29 year old woman comes to the clinic complaining of a three-day history of burning with urination and increased in urinary frequency.

00:19 She has suprapubic discomfort but no new vaginal discharge.

00:23 She's in a monogamous relationship with her husband and she's been sexually active with her last sexual encounter three days ago.

00:29 Her last menstrual period was about one week prior.

00:32 On exam, she's afebrile her blood pressures 118/72.

00:37 Pulse is 70.

00:38 Her exam is relatively unremarkable except for mild suprapubic tenderness to palpation but no costovertebral CVA tenderness to palpation or percussion.

00:48 The remainder of the exam is normal.

00:51 Her labs demonstrate on urine analysis has specific gravity of 1.02.

00:56 She's got trace blood and leukocyte esterase positive and nitrite positive as well.

01:02 So the question is, what is the most likely cause of this woman symptoms? Let's go through our case and see if we can find out.

01:09 So I think what's important in looking at the history.

01:12 She's complaining of dysuria that's burning with urination frequency and urgency along with suprapubic discomfort very suggestive of cystitis.

01:21 She also had sexual intercourse, which has been associated with UTIs in women.

01:26 And on exam, she's got mild suprapubic tenderness without having actual CVA tenderness suggestive of an isolated cystitis.

01:35 On urine analysis, we can see that having leukocyte esterase indicates the presence of white cells.

01:42 In nitrates indicate the presence of a gram negative organisms such as E. coli.

01:48 So the question is, what is the most likely cause of this patient symptoms an uncomplicated urinary tract infection or to be more specific cystitis.

02:00 So, what would be most appropriate in terms of the next step in management of this particular patient.

02:05 Given her symptoms, and given her urine analysis.

02:09 I think it's most appropriate to start empiric therapy.

02:12 So we can use empiric antibiotic therapy with nitrofurantoin or trimethoprim sulfamethoxazole.

02:18 So before we move on I think it's important to review some terminology and definitions.

02:23 Let's start with cystitis.

02:25 Cystitis is infection of the bladder or lower urinary tract.

02:30 Pyelonephritis is infection of the kidney or the upper urinary tract.

02:35 You'll also hear people talk about uncomplicated urinary tract infections.

02:39 This is infection in the urinary tract where there's no functional or anatomical abnormality.

02:44 There's no functional impairment or concomitant disease that would promote the UTI.

02:49 A complicated UTI on the other hand is when infection is associated with a structural or functional abnormality in the genitourinary tract.

02:57 Or the presence of an underlying disease that increases risk of acquiring an infection.

03:03 You'll also hear the term asymptomatic bacteriuria.

03:06 That means that you have presence of two separate consecutive clean voided urine specimens where there's 10 to the fifth or more colony forming units per milliliter of the same bacteria in the absence of symptoms.

03:19 Okay, so let's move on, when we think about who's vulnerable to UTIs.

03:24 There's five different demographic populations that we really need to consider.

03:28 First, urinary tract infection in children.

03:32 Second women in uncomplicated cystitis.

03:35 Third is women with recurrent cystitis.

03:38 And then fourth complicated urinary tract infections, and then finally asymptomatic bacteriuria.

03:45 So when we think about the pathogenesis of UTI in an uncomplicated infection, uropathogens are present in the rectal flora.

03:53 They can enter the bladder by the urethra.

03:56 We do see an increase in frequency in women and that's because of the smaller distance between the anus and the urethral meatus.

04:02 They're also hosts determinants that are involved in promoting an uncomplicated infection.

04:07 Behavioral.

04:08 This includes sexual intercourse recent antimicrobial use or suboptimal voiding habits.

04:13 So of people incompletely void.

04:17 Their genetic determinants as well, the innate and adaptive immune response is going to be important increased epithelial adherents of some of the bacteria and a prior history of recurrent cystitis will also play a role.

04:29 And finally, there are biological determinants the postmenopausal state or glycosuria particularly in diabetics.

04:38 How about an a complicated infection.

04:40 In terms of pathogenesis the same risk factors and host determinants from uncomplicated UTI play a role here as well.

04:47 But in addition these patients will often have a structural or functional abnormality of the genitourinary tract.

04:55 They can have obstruction or stasis of urine outflow or they might have impaired host defense.

05:01 This might be a patient whose immunosuppressed.

05:04 There's also an association with diabetes mellitus.

05:08 People with diabetes or going to be more prone to things like renal abscess.

05:12 Emphysematous pyelonephritis and xanthogranulomatous pyelonephritis, which we'll be talking about later.

05:19 So let's get back to our original clinical case that we were talking about.

05:22 Remember 29 year old women who came into the clinic complaining of cystitis.

05:27 Her symptoms of dysuria frequency and urgency were very suggestive of cystitis.

05:32 She had the right behavioral determinants.

05:34 She had recently had intercourse with her husband.

05:37 And on physical exam, she had signs of cystitis by having suprapubic tenderness.

05:42 We knew without having CVA tenderness and fever that she likely did not have pyelonephritis or infection of her kidney and her urine certainly looked as if there was infection with cystitis.

05:53 She had leukocyte esterase that was positive as well as nitrates, which were ended indicative of gram negative organisms.

06:00 So our question is, what microbial agent would most likely be the cause of her cystitis.

06:08 The answer is E. coli.

06:12 What if the patient though instead was a 68 year old gentleman who was hospitalized with a urinary catheter? Would E.coli still be the number one cause? We have to think about in that population.

06:24 Nosocomial were hospital-acquired infections those particular patients may need coverage for organisms such as methicillin-resistant staphylococcus aureus or MRSA.

06:36 So let's review the bacterial etiologies of urinary tract infections.

06:40 I want you to pay attention to these two tables that we have here.

06:43 The table on the left are gram negative organisms associated with UTIs.

06:47 The table on the right are gram-positive organisms.

06:50 And what I'd like you to note is that look at that first line.

06:54 E.coli by far and away is the number one cause of urinary tract infections and uncomplicated urinary tract infections.

07:03 It's to a lesser extent.

07:04 We see E.Coli and complicated UTIs, but one thing that you should note with complicated UTIs.

07:11 We tend to see some of the more obscure organisms like pseudomonas aeruginosa and some of the other enterobacter species as well.

07:19 For a gram positive organisms.

07:20 The most common that we see are going to be coagulase negative staph like staff saprophyticus and about 5 to 20% of uncomplicated UTIs.

07:28 Less so in our complicated UTIs, but we have an increase in enterococcus infections and complicated UTIs.