Review Urinary tract infection in pregnancy

1 2008 Royal College of Obstetricians and GynaecologistsReview2008;10:156 162 The Obstetrician & Gynaecologist156 Review Urinary tract infection in pregnancyAuthors Timothy McCormick/ Robin G Ashe/ Patricia M KearneyKey content: Urinary tract infection during pregnancy is common and is associated withsignificant maternal and perinatal morbidity and mortality. It can be asymptomatic. Screening of all women by urine culture should be performed in early pregnancy ,despite the cost. Treatment should be guided by urine culture and sensitivity reports. Antibiotic treatment should continue for 7 days, as shorter courses are not aseffective during objectives: To identify the clinical presentations. To understand the evidence base for effective investigation and issues: The empirical use of antimicrobial treatments increases drug resistance and mustbe balanced against delay in treatment and the associated acute cystitis/ asymptomatic bacteriuria/ pyelonephritis Please cite this article as: McCormick T, Ashe RG, Kearney PM.

2 Urinary tract infection in pregnancy . The Obstetrician & Gynaecologist2008;10:156 detailsTimothy McCormick MRCOGC onsultant Obstetrician and GynaecologistDepartment of Obstetrics and Gynaecology,Craigavon Area Hospital, 68 Lurgan Road, BT63 5QQ, UKEmail: author)Robin G Ashe FRCOGC onsultant Obstetrician and GynaecologistDepartment of Urogynaecology, Antrim AreaHospital, Bush Road, Antrim BT41 2RL, UKPatricia M Kearney FRCPath MScConsultant MicrobiologistDepartment of Microbiology and InfectionControl, Antrim Area Hospital, Antrim, 6/30/08 7:44 PM Page 156 IntroductionUrinary tract infection (UTI) is common inpregnancy. It can be asymptomatic, as well assymptomatic, complicating the diagnostic is of importance to obstetricians because of itsassociation with significant maternal and perinatalmorbidity and urine is sterile: therefore infection could,theoretically, be diagnosed if a single bacterium wasisolated from the Urinary tract .

3 In practice, voidedurine becomes contaminated in the nonsteriledistal urethra. Consequently, with logarithmicbacterial proliferation rates, most individualsdiagnosed with Urinary infection have bacterialcounts of 104 105/ml. Quantitative urine culture is,therefore, a necessity for among bacteriologists there is little consensuson the Urinary bacterial concentration that is trulydiagnostic of infection . Traditionally, the criterionof 105bacteria/ml has been used, as concentrationsat this level represent a chance of contamination of 1%. Use of the lower concentration of 104bacteria/ml is also appropriate1but, because of thehigher risk that it represents only bacterialcontamination rather than true infection , purity ofculture becomes the major determinant of anaccurate diagnosis.

4 Consequently, a diagnosis isonly made if a single strain of uropathogen (orpredominantly one with only very minorcontamination) is concentrations of 103 104bacteria/ml there is a50% chance that contamination is responsible;most laboratories request a repeat sample andculture. Isolation of the same organism in a secondculture is more indicative of significant diagnostic accuracy, it is essential thatcontamination is minimised. Sterile suprapubicbladder aspiration is the gold standard fordiagnosing UTI but the use of sterile cathetersamples can also reduce the contamination methods are, however, poorly tolerated bywomen and, therefore, impractical to consider inroutine antenatal practice. Random voided culturesare effectively useless because of very highcontamination rates.

5 The only pragmatic solution isto collect midstream samples of urine (MSSUs) aftercareful decontamination of the urethral Urinary tract infection in pregnancy has threeprincipal presentations (Box 1).IncidenceIn pregnancy , the overall incidence of UTI isapproximately 8%.2,3 The incidence ofasymptomatic bacteriuria in pregnant women asdetermined in UK studies is 2 5%.4 The incidenceof acute cystitis is more difficult to accuratelydetermine, as many women are treatedempirically and culture not performed. However,one study5over a 6-year period determined incidence rate. The incidence ofpyelonephritis during pregnancy is 2%, with upto 23% of women experiencing a recurrence inthe same is bacteriostatic to most local commensalbacteria and this is thought to result from itsrelatively acidic pH, high osmolality and high ureaconcentration.

6 In an anatomically normal urinarytract, sterility is maintained by free antegrade flowthrough the ureteral and urethral pregnancy , significant physiological changesoccur in the urogenital tract , increasing thepotential for pathogenic colonisation. Bladdervolume increases and detrusor tone , 90% of pregnant women developureteric dilatation as the result of a combination ofprogestogenic relaxation of ureteric smooth muscleand pressure from the expanding uterus. There isrelative sparing of the left ureter because ofprotection from the sigmoid colon and upperrectum. The net effect, however, is increasedurinary stasis, compromised ureteric valves andvesicoureteric reflux, which facilitates bacterialcolonisation and ascending percent of pregnant women developglycosuria and this, in combination withphysiological aminoaciduria of pregnancy and a fallin urine osmolality, favours bacterial activity in women has been established as asignificant risk factor for cantraumatise the urothelium of the distal urethra,resulting in increased bacterial invasion.

7 The vaginacan act as a reservoir for gastrointestinal bacteria,facilitating inoculation. In contrast with most157 Review2008;10:156 162 The Obstetrician & Gynaecologist 2008 Royal College of Obstetricians and GynaecologistsAAssyymmppttoommaattiicc bbaacctteerriiuurriiaaDefined as persistent colonisation of the Urinary tract by significant numbers of bacteria in women without Urinary ccyyssttiittiissDistinguished from asymptomatic bacteriuria by the presence of symptoms such as dysuria, urgency, frequency, nocturia, haematuria and suprapubic discomfort in afebrile women with no evidence of systemic as significant bacteriuria in the presence of systemic illness and symptoms such as flank orrenal angle pain, pyrexia, rigor, nausea and 1 Classification of Urinary tractinfection in 6/30/08 7:44 PM Page 157158 Review2008.

8 10:156 162 The Obstetrician & Gynaecologist 2008 Royal College of Obstetricians and Gynaecologistsvulval and perineal commensal bacteria, Gram-negative bacteria from the bowel thrive in , most Urinary infections are causedby aerobic Gram-negative bacilli from thegastrointestinal tract . Difficulty with hygienebecause of a distended, gravid abdomen canexacerbate the role of immune system status during pregnancyin organism pathogenicity remains immunity undergoes modification,favouring the implantation and development of theembryo. Research10suggests that the immuneresponse is modulated from a cell-mediated to ahumoral response. This mechanism does not solelyrely on the recognition of cell-surface majorhistocompatibility complex (MHC) proteins,resulting in less efficient responses to bacterial cellsurface proteins and possibly facilitatingpathogenicity.

9 While it is a misconception to depictpregnancy as an immunodeficient state,theoretically, these changes allow uropathogens toinfiltrate, proliferate and ascend prevalence of infection increases with age andlower socioeconomic grouping. Concomitanturinary tract anomalies and maternal disease (forexample, diabetes or sickle cell disease) alsosignificantly increase , it must be remembered that medicalinterventions during pregnancy can result innosocomial infection ; for example, urethralinstrumentation and catheterisation predispose toascending bacteria causing Urinary infection in pregnancyessentially mirror those in nonpregnant coliaccounts for 80 90% of infections11but other Gram-negative bacilli, such as Proteusmirabilisand Klebsiella pneumoniae, can be , Klebsiellaand most Enterobacteriaceaespecies show urease activity and form urinarycalculi, which can act as reservoirs of infection .

10 Thecoagulase negative cocci,Staphylococcussaprophyticus, is the second most frequently cultureduropathogen,12while other Gram-positive cocci,such as group B haemolytic streptococci, are lessfrequently isolated but remain clinically less common uropathogens includeStaphylococcus aureusand Mycobacteriumtuberculosis, which can arise via haematologicalinoculation rather than ascending causes include Chlamydiaspecies andfungal infections, such as Candida B streptococcal infectionVaginal colonisation with group B streptococci isstrongly associated with preterm rupture ofmembranes, labour and delivery and is a provencause of neonatal sepsis. Evidence relating group Bstreptococcal bacteriuria with similar consequencesis less well ,15 However, treatment forurinary group B streptococcal infection isassociated with a significant reduction in preterm,prelabour rupture of membranes and are referred to the Royal College ofObstetricians and Gynaecologists (RCOG)guideline17pertaining to prophylaxis of group Bstreptococcal manifestations Asymptomatic bacteriuriaIn 1962, Edward Kass18observed significantbacteriuria in 6% of asymptomatic pregnantwomen presenting for their first antenatal discovered that untreated asymptomaticbacteriuria was associated with adverse maternaloutcomes, including symptomatic cystitis (up to30%), pyelonephritis (up to 50%)