Evaluation of Infection In Pregnancy

KARKI, BIJAY KUMARMEDICAL LABORATORY STUDENT

• IN pregnant women, most infections are no more serious than in non- pregnant women of similar age

some infections can be transmitted to the fetus in utero or to the infant during or immediately after delivery, with potentially serious sequale.

Uncommonly, serious infectious illness in the mother can have non- specific fetal or obstetric effects and lead to miscarriage, premature labour or fetal death, these infections must be treated as any other serious illness. more common and a source of anxiety is mild illness or suggestive

laboratory findings in the absence of symptoms.

Intra amniotic infection due to bacteria in the vaginal flora not only initiate labor but can also cause infections such as septicemias and meningitis in the new born.

Several host defense mechanisms operate against ascending infections:

»Vaginal acidity»Cervical mucus»Intact membranes»Antibacterial activity of amniotic fluid

• Organisms causing neonatal sepsis

Early onset sepsis ( 24 hours to 7 days postpartum):Streptocococcus B- haemolyticus (GBS)E. coli

Late onset sepsis ( later than 7 days postpartum):Coagulase negative staphylococcus (CONS)Streptococcus B- haemolyticus (GBS)Staphylococcus aureus

Streptococcus B- haemolyticus of group B of lanncefield (SGB) or streptococcus agalactiae

The prevalence of SGB colonization among pregnant women ranges from 10 to 30 %

SGB disease can occur in three clinical forms: Early onset disease,, defined by the development of disease in newborn

infants up to the 7 th day of llife Late onset disease, charaterized by occurense between the 8 th day and

3rd month of life. Very late onset disease, occurring after the 3 rd month of life

Prevention: SGB culture for women at between 35 and 37 weeks of gestation – antibiotic therapy if culture is positive

• Infection jeopardizing the fetus with no serious maternal consequences.

o Cytomegaloviruso Toxoplasmosiso Parvovirus B19

Infections jeopardizing the fetus with possible maternal complications

oRubella oVaricellaoSexually transmitted infectionsomalaria

cytomegalovirus Cytomegalovirus is the leading cause of congenital viral

infection

Typical clinical syndromes : intrauterine growth restriction, microcephaly, hepato splenomegaly, petechiae, jaundice, thrombocytopenia, anemia, chorioretinitis

Long term neurodevelopmental sequale include: mental retardation, motor impairment, sensorineural hearing loss and/ or visual impairment

Primary maternal CMV infection during gestation poses a 40 % risk of intrauterine transmission

Toxoplasmosis Detection of T. gondii –specific IgM antibodies has been used

as an aid in determining the time of infection: a negative IgM test result with a positive IgG result usually indicates infection at least six months previously.

When a pregnant women is found to be infected with T. gondii, the next step is to determine whether the fetus is infected: PCR testing of amniotic fluid is used to diagnose congenital toxoplasmosis.

Parvovirus B19• Most persons ( usually children: erythema infectiosum or fifth

disease) with parvovirus B19 infection are asymptomatic or have mild, nonspecific, cold like symptoms.

• The virus is highly infectious and spreads mainly through respiratory droplets.

• The infection can trigger an acute cessation of RBC production, causing transient aplastic crisis, chronic red cell aplasia, hydrops fetalis, or congenital anemia.

• Although the virus can be contracted in any trimester, the second trimester seems to carry the highest risk of fetal loss

To test a fetus for possible infection , a PCR is performed on amniotic fluid.

Fetal cord blood is not widely used because of the associated 1 % fetal loss rate, and also because the IgM does not often appear in the fetal circulation until after 22 weeks gestation.

Routine prenatal screening for parvovirus B19 is not advised. If the fetus shows evidence of hydrops, the only treatment option is intrauterine blood transfusion to correct the assosciated anemia.

Rubella infection The earlier in gestation the maternal infection occurs,, the more

severe is the damage to the fetus. Maternal infection during the first 8 weeks after the last

menstrual period results in nearly all fetus becoming infected and upto 100% of infected fetus developing congenital defects: Congenital heart diseases Congenital cataract Deafness Microcephaly Mental retardation

The risk of fetal infection and the severity of congenital abnormalities decreases after the 1st trimester, after 17 weeks gestation, the risk of developing any defect is low

Varicella – zooster virus VZV is spread by respiratory transmission or direct contact with

infectious lesion. At any stage during pregnancy, severe maternal chickenpox

may cause intrauterine death. Varicella infection in the first and second trimesters may lead to

the congenital varicella syndrome The symptoms include:

Skin lesion in dermatomal distribution Neurological defects Eye diseases Skeletal anomalies

About 30% of infants born with these lesion die in the 1st trimester of life

Pregnancy outcomes following maternal sexually transmitted infections

Neonatal herpes:

pulmonary diseases, seizures, fever, intracranial findings, a high fatality rate

Gonococcal infection:

preterm delivery, premature rupture of the membrane, LBW, postpartum endometritis, gonococcal opthalmia neonaturum

Chlamydia infection:

preterm delivery, LBW, infant pneumonia Trichomonas infection:

preterm delivery, LBW Bacterial vaginosis: Syphilis

Ureaplasma urealyticum Ureaplasmal colonization of the lower genital tract is not

assosciated with adverse pregnancy outcome. Ureaplasmal infection of the chorioamnion have been

implicated in :

o Infertilityo Spontaneous abortiono Still birtho Premature birtho LBWo Increased perinatal morbidity and mortality

U. urealyticum is the single most common mos. Isolated from

the CNS and LRT of newborn infants

Malaria in pregnancy• Women living in endemic areas are considered to have some

immunity and malarial infections are usually asymptomatic.

• The disease is almost always symptomatic, and potentially lethal, in non immune patients particularly gravid females.

• Possible pregnancy complications. Preterm delivery IUGR Spontaneous abortion Still birth Postpartum haemorrhage Puerperal fever Maternal / fetal death

Screening of infections Universal screening of pregnant women should be

recommended for the following :

Syphilis Chlamydia, ureaplasmal infection and gonorrhea or

bacterial vaginosis SGB culture for women at between 35 and 37 weeks of

gestation HIV Testing history of genital and orolabial herpes simplex V virus

infection rubella history of chickenpox vaccination

Routine screening for toxoplasmosis, cytomegalovirus or parvovirus infection is not recommended.

CHANGES IN PREGNANCY

• Increased renal parenchymal volume due to intrarenal fluid accumulation, hence…

• massive dilatation of renal calyces and ureter. [approximately 90 % of pregnant women develop ureteral dilatation, which will remain until delivery, and up to 12th – 16th postpartum week.]

• By 2nd trimester, there is increased renal blood flow up to 70-80 % and also GFR by 45-50%.

• Diagnosing intra amniotic infection intra amniotic infection is difficult to diagnose on the basis of any single criterion

and so diagnosis depends on a set of criteria, the most important clinically being maternal fever and tachycardia and fetal tachycardia.

Increased maternal leukocyte count , fetal biophysical profile examination using ultrasound are also used in diagnosis.

Detection and estimation of surrogate markers:• C- reactive protein• Cytokines • Fetal fibronectin

The infection may be polymicrobial, but collecting amniotic fluid samples without contamination with normal vaginal flora is cumbersome and may require invasive procedures.

After membrane rupture many bacteria may enter the amniotic cavity without having caused the rupture

UTI• An urinary tract infection (UTI): Bacteriuria:

i] presence of at least 100,000 organisms/mL of urine in an asymptomatic patient

ii] as more than 100 organisms/mL of urine with accompanying pyuria (>7 WBCs/mL) in a symptomatic patient

can be lower/upper UTI

• Pregnant women are at increased risk for UTI's starting in week 6 through week 24.

Essential Elements of Urine Cultures• Pathophysiology of urinary tract infection

• Microbiology of urinary tract infection

• Clinical signs and symptoms of urinary tract infection Technical variables in specimen collection and transport

• Interpretation of urine cultures

• Quality management

Pathophysiology of urinary tract infection• Ascending route of infection most common

• Colonization of urethra and periurethral tissue by uropathogens the initial event in urinary tract infection

• Urinary tract infection more common in women than men due to short female urethra with distention and turbulent flow that washes urethral organisms into the bladder during micturition and in close proximity to perianal areas

• Hospital infection associated with lower urinary tract instrumentation (catheterization, cystoscopy)

• Once in the bladder uropathogens multiply, then pass up the ureters (especially if vesicoureteral reflux present) to the renal pelvis and parenchyma

• Source of uropathogens: enteric bacteria

Pathophysiology of urinary tract infection• Cystitis: localized infection of the bladder with superficial

neutrophilic inflammation of the mucosa (lower urinary tract infection)

• Pyelonephritis: infection of the kidney with acute suppurative inflammation of the pelvis, medullary and cortical tubules, and corticomedullary intersititum (upper urinary tract infection)

• Urosepsis: bacteremia due to pyelonephritis

• Papillary necrosis: complication of pyelonephritis in diabetes and urinary tract obstruction with coagulative necrosis of renal pyramids and an intense inflammatory response between preserved and necrotic tissue

• Sloughing of necrotic pyramids: complication of papillary necrosis that can cause urinary tract obstruction (in some instances sloughed portions voided and recovered in urine)

• Perinephric abscess: associated with obstruction of an infected kidney with abscess formation in the pernephric space due to extension of bacterial infection across the renal capsule

Pathophysiology contd……

• Uncomplicated urinary tract infection: Bacterial or yeast infection in a structurally and neurologically normal urinary tract

• Complicated urinary tract infection: Bacterial or yeast infection in a urinary tract with functional or structural abnormalities

Risk factors in complicated urinary tract infection

• Indwelling catheters• Urinary calculi• Neurogenic bladder• Prostatic enlargement• Uterine prolapse • Urologic instrumentation or

surgery• Renal transplantation• Diabetes mellitus

Bacterial virulence factors in urinary tract infection• Escherichia coli strains expressing O-antigens O1, O2,

O4, O6, O7, O8, O75, O150, and O18ab cause high proportion of infections

• Capsular K1, K5, and K12 antigens of E. coli associated with clinical severity (antiphagocytic)

• P-fimbriae enhance mannose-resistant attachment of E. coli to globoseries glycosphingolipid receptors (gal-gal) of uroepithelial cells (P-fimbriated E. coli dominant as cause of pyelonephritis and urosepsis)

• Type 1 fimbriae enhance mannose-susceptible adherence of E. coli to uroepithelial cells (virtually all cystitis-producing E. coli strains express type 1 fimbriae)

• Motile bacteria ascend the ureter against urine flow

Bacterial virulence factors in urinary tract infection

• Bacterial urease (Proteus, Corynebacterium urealyticum) splits urinary urea with generation of ammonium ion that alkalinizes urine with loss of acid pH as natural defense barrier against infection, stone formation with ureteral obstruction and survivial of bacteria deep within stones resisting eradication by antibiotic, and alkaline-encrusted cystitis

• Gram-negative endotoxin decreases ureteral peristalsis• Hemolysin produced by many uropathogens damages

renal tubular epithelium and promotes invasive infection

• Aerobactin (a siderophore) present at increased frequency in uropathogenic strains of E. coli promoting intracellular iron accumulation for bacterial replication

Host protective factors in urinary tract infection

• Flushing mechanism of micturition a major protective factor

• Low vaginal pH (3.5-4.5) (due to lactic acid produced by action of Lactobacilli on glycogen of sloughed vaginal epithelial cells) suppresses colonization by uropathogens

• Normal acid pH of urine (4.6-6) anti-bacterial • Urinary Tamm-Horsefall protein (secreted by ascending

loop of Henle) binds to mannose-sensitive fimbriae and blocks E. coli attachment to uroepithelial cells

• Chemotactic interleukin-8 released upon bacterial attachment to uroepithelial cells with recruitment of phagocytic neutrophils and eradication of bacteriuria

Pathophysiology of urinary tract infection• Hematogenous seeding of renal cortex less frequent

than ascending infection

• Kidney a common site of abscess formation in Staphylococcus aureus bacteremia, less often in candidemia, rarely with gram-negative bacteremia

• Hematogenous seeding of kidney also occurs with Salmonella (typhoid) and Mycobacterium tuberculosis

• Evidence for a role of periureteral and renal lymphatics in urinary infection lacking

Common Uropathogens• Escherichia coli• Other Enterobacteriaceae (Klebsiella, Enterobacter,

Proteus, Citrobacter)• Pseudomonas aeruginosa• Enterococcus• Staphylococcus saprophyticus• Staphylococcus aureus1

• Streptococcus agalactiae (group B)2

• Candida1Associated with staphylococcemia2Denotes vaginal colonization in pregnant women

Uncommon Uropathogens• Corynebacterium urealyticum1

• Haemophilus influenzae and H. parainfluenzae2

• Blastomyces dermatitidis3

• Neisseria gonorrhaeae4

• Mycobacterium tuberculosis5

1Colistin nalidixic acid (CNA) agar2Chocolate agar3Brain heart infusion, inhibitory mold, or Sabourad

dextrose agar4Enhanced recovery with chocolate agar5Lowenstein-Jensen medium, Middlebrook broth or

agar

Commensal Microflora of the Urethra

• Coagulase-negative staphylococci (except S. saprophyticus)

• Viridans and non-hemolytic streptococci• Lactobacilli• Diphtheroids (Corynebacterium except C.

urealyticum)• Saprophytic Neisseria• Anaerobic bacteria

Common Risk Factors for Urinary Tract Infection: Women

– Urinary tract obstruction (including calculi)– Catheterization (straight, indwelling)– Pregnancy– Urologic instrumentation or surgery– Neurogenic bladder– Renal transplantation– Sexual intercourse– Estrogen deficiency (loss of vaginal lactobacilli)

Signs and Symptoms of Lower Urinary Tract Infection

• Inflammatory irritation of urethral and bladder mucosa

• Frequent and painful urination of small volumes of turbid urine

• Occasional suprapubic pain or sensation of heaviness

• Fever generally absent

Signs and Symptoms of Upper Urinary Tract Infection

• Fever and chills (systemic reaction)

• Flank pain

• Lower urinary tract signs and symptoms (frequency, urgency, and dysuria)

Asymptomatic Bacteriuria

• Presence of uropathogens by culture without signs or symptoms of urinary tract infection

• Clinically significant (should be treated) with preschool children (? vesicoureteral reflux, congenital urinary tract anomaly), pregnant women, and adults with obstructive uropathy

• Without clinical significance (should not be treated) for adults in absence of urinary tract obstruction

Urinary Tract Specimens• First-voided morning urine optimal (generally

bacteria have been proliferating in bladder urine for several hours)

• Midstream urine specimens (initially voided urine contains urethral commensals)

• Indwelling catheters (freshly placed, urine aspirated by needle inserted into catheter) (Foley catheter tips not acceptable)

• Straight catheter specimens• Suprapubic aspirates (infants or children, recovery

of anaerobes)1

• Cystoscopic collection of urine

1Contamination-free specimen

Collection of Urine Specimens

• Urine collected in sterile specimen container must be processed within 2 hours, or refrigerated and processed within 24 hours

• Urine collected in sterile specimen container with borate preservative should be processed within 24 hours (no refrigeration required)

Inoculation of Urine• Inoculation of urine for quantitative culture (colony forming

units→cfu’s) performed with a calibrated 0.001 mL and 0.01 mL plastic or wire loop

• Sheep blood agar (SBA) utilized for quantitative urine culture

• With 0.001 ml loop, 1 colony on SBA equivalent to 1,000 cfu’s per mL of urine

• With 0.01 ml loop, 1 colony on SBA equivalent to 100 cfu’s per mL of urine

• MacConkey agar utilized as selective differential agar for gram-negative bacteria, colistin nalidixic acid agar as selective agar for gram-positive bacteria, and chocolate agar for fastidious gram-negative bacteria (Haemophilus)

Interpretation of Urine Cultures: General Guidelines

• A single species of Enterobacteriaceae recovered at >105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 95% probability of true bacteriuria

• A single species of Enterobacteriaceae recovered at 104-105 cfu’s/mL urine: with patients symptomatic for urinary tract infection, 33% probability of true bacteriuira

• Gram-positive, fungal, and fastidious uropathogens often present in lower numbers (104-105 cfu’s/mL urine)

• Urethral commensals recovered at <104 cfu’s/mL urine

Cumitech Guidelines for Inoculation of Urine Cultures1

• Routine: uncomplicated urinary tract infection in ambulatory outpatients (0.001 mL loop, SBA, MAC; 24 hr incubation)

• Surveillance: neurogenic bladder, indwelling catheter, geriatric patents (0.001 mL loop, SBA, MAC, CNA; 24 hr incubation)

• Special: suprapubic aspirates or straight catheter specimens where previous cultures negative, unresponsive to therapy, or possibility of unusual urinary tract pathogen (0.001 and 0.01 mL loop, BA, MAC, CHOC; minimum 48 hr incubation)

1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM Cumitech 2B, November 1998.

Cumitech Guidelines for Interpretation of Routine Urine Cultures1

• One isolate at >104: Full ID and Susceptibility

• One or two gram-negative isolates at >105 and other isolates at least 10X less: Full ID and Susceptibility of gram-negative isolates

• Other patterns of isolates at >104: Presumptive ID only

• Ignore mixed urethral flora at <104

1Clarridge, Johnson, Pezzlo, and Weissfeld, ASM Cumitech 2B, November 1998.

Cumitech Guidelines for Interpretation of Surveillance Urine Cultures1

• One isolate at >104: Full ID and Susceptibility

• One gram-negative isolate at >105 with others at least 10X less: Full ID and Susceptibility

• Other patterns of isolates at >104: Presumptive ID only

• Ignore mixed urethral flora at <104

• One or two isolates at >102 to 105: Full ID and Susceptibility

1Clarridge, Johnson, Pezzlo, and Weissfeld, Cumitech 2B, November 1998

ASM Manual Guidelines for Urine Culture Results Likely to Be Significant1

• Midstream, female with cystitis, >102 with positive urine leukocyte esterase

• Midstream, female with pyelonephritis, >105 with positive urine leukocyte esterase

• Midstream, asymptomatic, >105 with negative urine leukocyte esterase (usually)

• Midstream, male with UTI: >103 with leukocyte with urine leukocyte esterase positive

• Straight catheter: >102 with urine leukocyte esterase positive

• Indwelling catheter: >103 with urine leukocyte esterase positive or negative

1Manual of Clinical Microbiology, 8th Edition, ASM, 2003

NMH Guidelines for Interpretation of Urine Cultures1

Urine leukocyte esterase positive

One or two organisms at >103: Full ID and Susceptibility

One organism at >104 with others (2 or more) at least 10X less: Full ID and susceptibility of predominant organism

Report all group B β-hemolytic streptococci for women < 50 years

1Modified from ASM Cumitech, ASM Manual, and CDC MMWR 2002;51 (RR-11):1-22

COMPLICATION

 UTIs are associated with risks to both the fetus and the mother

* pyelonephritis * preterm birth * low birth weight * increased perinatal mortality

Prevention• Drink 6-8 glasses of water each day and eliminate

refined foods, fruit juices, caffeine, alcohol, and sugar.

• Take Vitamin C (250 to 500 mg), Beta-carotene (25,000 to 50,000 IU per day) and Zinc (30-50 mg per day) to help fight infection.

• Develop a habit of urinating as soon as the need is felt and empty your bladder completely when you urinate.

• Urinate before and after intercourse.

• Avoid intercourse while you are being treated for an UTI.

• After urinating, blot dry (do not rub), and keep your genital area clean. Make sure you wipe from the front toward the back.

• Avoid using strong soaps, douches, antiseptic creams, feminine hygiene sprays, and powders.

• Avoid wearing tight-fitting pants.

• Don't soak in the bathtub longer than 30 minutes or more than twice a day.

References• Sobel and Kaye. Urinary Tract Infections. In

Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 6th edition, Elsevier, 2005, pp. 975-905.

• Clarride, Johnson, Pezzlo, and Weissfeld. Laboratory Diagnosis of Urinary Tract Infections. Cumitech 2B, ASM Press, 1998, pp. 2-19.

• Thomson, Jr. and Miller. Specimen Collection, Transport, and Processing: Bacteriology. In Manual of Clinical Microbiology, 8th edition, ASM Press, 2003, pp. 286-330.

• Chapter 60. Infections of the Urinary Tract. In Bailey & Scott’s Diagnostic Microbiology, 11th edition, Mosby, pp. 927-938,

Thank You For Sincerely Paying Attention…