Abstract 

Objective: To determine the prevalence of asymptomaticbacteriuria, bacteriology and sensitivity pattern in Ilorin using thegold standard of urine culture.

Methods: A prospective study was carried out from 1st Julyto 31st October 2007, at the University of Ilorin TeachingHospital (UITH) on 125 consenting asymptomatic pregnantwomen. A structured proforma was used to collect informationfrom the women and a midstream urine specimen collected forbacteriological culture.

Results: Of the 125 pregnant women, 50 had bacteriuria on urineculture giving a prevalence of 40%. The mean age of the womenwas 28.5 years with a standard deviation of 4.95. The age rangedbetween 14 and 40 years. Staphylococcus aureus was the commonestpathogen isolated (72%), followed by Proteus spp (14%). Most ofthe organisms showed good sensitivity to Nitrofurantoin andgentamicin.

Conclusion: The prevalence of asymptomatic bacteriuria in Ilorinis high and routine urine culture is advocated for all pregnantwomen at booking.

Keywords: Asymptomatic bacteriuria; Pregnancy; Prevalence; Urine culture; Sensitivity.

Introduction

The urinary tract is second only to the respiratory tract in acquiring microbial infections, especially in females. Urinary tract infections (UTI) are more common in pregnant than non-pregnant women.^1,2 Asymptomatic bacteriuria (ASB) is defined as the presence of actively multiplying bacteria in the urinary tract excluding the distal urethra in a patient without any obvious symptoms.³ This is confirmed in the presence of significant bacteriuria based on isolation of ≥10⁵ cfu/ml of same species of bacteria in properly collected and transported midstream urine during a screening test.^3-8

Several studies have shown the overall prevalence of asymptomatic bacteriuria in pregnancy to be between 2-7%,^3,5,8-13 but may be as high as 10% in high risk populations.^9,14,15 It is twice as common in pregnant women with sickle cell trait and three times as common in pregnant women with diabetes mellitus as in normal pregnant women.^3,9,14,16 Other conditions associated with increased incidence include low socio-economic status, grandmultiparity and advancing age.^10,17 However, several studies have shown that the prevalence of ASB in developing countries is higher than in the developed countries.

The significance of asymptomatic bacteriuria in pregnancy lies in its potential to cause acute pyelonephritis, preterm labor and preterm rupture of membranes. Others include anemia, pre-eclampsia, chronic pyelonephritis and even fetal wastage.^5,18-21 It is associated with acute pyelonephritis in 25-30% of pregnant women compared with 1-2% in those without asymptomatic bacteriuria.^7,8,22,23

This study assessed the prevalence of ASB among pregnant women attending antenatal care in University of Ilorin Teaching Hospital.

Methods

This was a prospective descriptive study amongst asymptomatic pregnant women attending their first antenatal clinic visit, at the Maternity wing of the University of Ilorin Teaching Hospital, Ilorin between July and October, 2007. Systematic random sampling technique was employed in recruiting 125 subjects who met the stated criteria. A structured profoma containing information on bio-data was administered on all recruited subjects at booking, and physical examination was done by medical personnel on the research team after obtaining informed consent. Subjects were informed of their results and those with positive culture were treated with a course of antibiotics based on the sensitivity pattern and duly followed up in the clinic to ensure bacteriological cure. The study was approved by the Ethical Research Committee of the Hospital.

Laboratory Procedure

About 5 ml of midstream urine was collected into a sterile universal bottle and the sample taken to the microbiology laboratory for microscopy and culture within 2 hours of collection.

Urine Microscopy & Culture

A loop full of well-mixed centrifuged urine was examined under wet preparation procedure to detect pyuria, while noting red cells, casts, parasites and fungi, when present. Urine culture was done with 0.001 ml of well mixed urine delivered by a sterile calibrated wire loop and plated on CLED and blood agar plates, which were incubated aerobically at 35-37^oC for 24 hours. Repeat culture was ordered for contaminated specimens. Each significant isolate was identified by colonial morphology, gram staining and biochemical reactions according to standard procedure.²⁴ Antibiotic sensitivity testing was done by emulsifying selected isolates in normal saline at a turbidity compared to 0.5 Mac Farland’s standard. Using sterile swabs, suspensions were inoculated on Muller-Hinton agar in accordance with modified Kirby-Bauer method and incubated at 35-37^oC for 18-24 hrs. Single antibiotic impregnated discs including; gentamicin (10 µg), amoxicillin (25 µg), augmentin (30 µg), nalidixic acid (30 µg), nitrofurantoin (300 µg), erythromycin (5 µg), cotrimoxazole (25 µg), ceftazidime (30 µg) and cefuroxime (30 µg) were tested against gram-positive and gram-negative organisms as appropriate. Interpretation was done by comparing the diameter of zone of inhibition with those of a standard table in three grades of susceptibility which are sensitive, intermediate and resistant.

Control strains of Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) were run with the gram-positive and gram-negative isolates, respectively. All procedures were done as recommended by the Clinical Laboratory Standard Institute (CLSI).²⁵ Information obtained were recorded on a data collection sheet designed for the study, and fed into the computer using EPI-INFO version 3.3.2 software package for data analysis.

Results

A total of 125 consenting pregnant women who met the inclusion criteria were studied. The socio-demographic characteristics of the women screened are illustrated in Table 1. Their age ranged between 14 and 40 years with a mean age of 28.5+ 4.95. The median and modal ages were 28 and 30 years respectively. Most of the women, (94.4%) were married, while 5.6% were single. The table also shows that majority (64.8%) of the women had tertiary education. Also, 3.2% of the women had no formal education, while 4% and 28% had primary and secondary education respectively. Forty-seven (37.6%) were Christians while 78 (62.4%) were Muslims. The parity of the women ranged between zero and six, with the modal parity of zero. Forty-nine (39.2%) women were nulliparous, while 47.2% belonged to the para 1-2 group. Three (2.4%) women were grandmultiparous. The gestational age of these women ranged between 9 and 24 weeks with a modal gestational age of 17 weeks. Forty-one (33.3%) had a gestational age between 17 and 20 weeks, while 17.9% had gestational age between 9 to 12 weeks.

Table 1: Sociodemographic characterisctics of women screened for asymptomatic bacteriuria.

Table 2 shows the results of the urine culture of the 125 pregnant women screened. A total of 50 women had asymptomatic bacteriuria on urine culture, giving a prevalence of 40%. Thirty-five (28%) had no growth on culture, while 40 women (32%) had insignificant bacteriuria. Twelve women had mixed growth which was repeated and subsequently were classified into one of the above three groups. None of the women with asymptomatic bacteriuria had any medical illness.

Table 2: Results of urine culture.

The profile of bacteria isolated from cases of significant bacteriuria is shown in Table 3. Staphylococcus aureus constituted the commonest cultured organism, 36 (72%). This was followed by Proteus spp. 7 (14%). Other isolates included Staphylococcus epidermidis 3 (6%), Klebsiella spp. 2 (4%) and Escherichia coli 2 (4%).

Table 3: Profile of bacteria isolated from cases of significant bacteriuria.

The sensitivity pattern of organisms cultured from the cases of significant bacteriuria is illustrated in Table 4. Staphylococcus aureus, the commonest isolate showed good sensitivity to gentamicin and nitrofurantoin with 75% and 77.8% of the organisms respectively. Proteus spp showed good sensitivity to gentamicin, nalidixic acid, ceftazidime and cefuroxime. Most of the organisms showed good sensitivity to Nitrofurantoin and gentamicin.

Table 4: Sensitivity pattern of organisms cultured from cases of significant bacteriuria.

- not tested; S- sensitive; R- resistance; Is-intermidiate sensitivity.

Discussion 

The patients involved in the study though recruited randomly at booking were mainly between 21-30 years of age, this being about the peak reproductive period in this environment and most societies. Most of the women (94.4%) were married and this could be associated with the higher chance of pregnancy being planned and thus presentation for antenatal care compared to singles. The literacy rate was quite high with 64.8% having tertiary education and 28% having secondary education. The women were also mainly of low parity (86.4%). These were both in keeping with other studies which found antenatal booking to be high in women with at least secondary school education and low parity.^26,27 Of the women recruited, 62.4% were Muslims and 37.6% Christians, Ilorin being a predominantly Muslim community. Fifty-one percent (51%) of the Christians and 33% of the Muslims had positive culture results. The lower prevalence in the Muslims might be attributed to rinsing of the vulva following every episode of urination, practiced in the religion. However Sescon et al. found low socio-economic status, high parity and advancing age to be associated with increased prevalence of asymptomatic bacteriuria in pregnancy.⁴ McNair et al.²⁸ and Akinloye et al.²⁹ found an increased association of asymptomatic bacteriuria with parity.

This study found 50 cases of significant bacteriuria among the 125 pregnant women at UITH giving a prevalence rate of 40%. This is higher than the reported prevalence from Lagos, Ibadan, Sagamu and Ile-Ife of 4%, 12%, 23.9% and 26%, respectively.^22,30-32 This high prevalence might be due to the fact that only women who booked around the peak gestational age for bacteriuria were recruited for the study. It was however lower than the prevalence of 86.6% reported by Akerele in Benin.³³ These differences may also be attributed to variation in population characteristics such as age, parity, socio-economic status and bacterial ecology.

The strength of the study lies in the fact that measures were taken to ensure that urine samples were appropriately collected and analyzed within two hours of collection. The most common organism isolated was Staphylococcus aureus which was isolated from 36 (72%) cases. This was followed by Proteus spp. 7 (14%), Staphylococcus epidermidis 3 (6%), Klebsiella 2 (4%) and Escherichia coli 2 (4%). This was consistent with the findings by Akerele in Benin,³³ and Oyagade in Ado-Ekiti,³⁴ who also found Staphylococcus aureus as the predominant isolate.

Most of the organisms were very sensitive to nitrofurantoin, gentamicin, cefuroxime and ceftazidime. Resistance to cotrimoxazole and amoxicillin were relatively high. Results showed that 77.8% of Staphylococus aureus, 100% of Staphylococcus epidermidis, Klebsiella and Escherichia coli were sensitive to Nitrofurantoin; while Staphylococcus aereus and Proteus spp. showed 75% and 85.7% sensitivity respectively to gentamicin. Both antibiotics were also found to be highly effective in studies by Mandara in Zaria,¹² Ezeome in Enugu,³⁵ and Tupin in Ghana.³⁶ Mezue et al.³⁷ at the University of Nigeria found Cotrimoxazole to be virtually useless against pathogens that cause UTI. Amoxicillin and augmentin were only slightly better. A clear alternative as a first line drug against UTI before culture and sensitivity is Nitrofurantoin.^37,38 Gupta et al. stated that nitrofurantoin is relatively safe in pregnancy and is effective against most urinary tract infections but may cause hemolysis in glucose-6-phosphate dehydrogenase deficient infants if used close to term.³⁶ There is some reluctance among doctors to prescribe nitrofurantoin and this may be due to its side effect profile, but it is clearly an important drug for urinary tract infections. 

Conclusion 

Overall, the prevalence of asymptomatic bacteriuria in our locality at 40% is high. Therefore, screening for and treatment of asymptomatic bacteriuria in pregnancy should be an integral part of obstetric care and should be included in all antenatal guidelines.

Acknowledgements

The Authors are grateful to the University of Ilorin Teaching Hospital for its financial contribution in carrying out the study. The study was approved by the Ethical Research Committee of the Hospital. No conflict of interest exists.

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