Study design and setting
This was a cross-sectional study carried out between March and September 2020 to assess factors associated with extended-spectrum β-lactamase producing Enterobacteriaceae in randomly selected community patients attending outpatient health centres in Blantyre, Malawi. Three health centres were selected randomly. They included Limbe, Zingwangwa and Ndirande health centres.
Study population, Sample collection and laboratory procedures
The study participants comprised of 300 adult (≥18 years old) community patients. Participats present on the day of data collection were recruited randomly into the study regardless of their reason to seek health care. Social demographic characteristics and clinical data including age, sex, education, occupation, history of prior hospitalization, history of surgery and prior history of antibiotic use were collected using a standadard questionnaire. From each participant, either rectal swab or urine sample was collected for ESBL-E screening. Urine samples were collected exclusively from patients that had complained of UTI symptoms. Samples were taken using standard microbiological procedures and were immediately sent to the microbiology laboratory of the College of Medicine University of Malawi for processing.
Initial screening for potential ESBL-producing Enterobacteriaceae was performed by culture on chromogenic selective medium (CHROMagarTM ESBL) supplemented with ESBL supplement containing a selective mixture of antibiotics enabling selective growth of ESBL-producing Enterobacteriaceae and inhibiting the growth of non-ESBL Enterobacteriaceae (CHROMagarTM, Paris, France). The putative culture of ESBL producers was phenotypically confirmed using combination disk test method (CDT) by comparing the inhibition zone diameter around cefotaxime (CTX-30μg) and ceftazidime (CAZ-30μg) disks with and without clavulanic acid as previously described [24].
Biochemical identification of Enterobacteriaceae
Presumably, identification of common ESBL-producing Enterobacteriaceae isolates was first done based on bacterial colonial morphology and chromogenic characteristics on CHROMagarTM medium plates according to the manufactures’ instructions. Subsequently, the identity of Enterobacteriaceae was confirmed using the commercially acquired biochemical substrate strips (Microbact™, Oxoid, GNB 12A) according to the manufacturer’s instructions.
For quality control purposes, ESBL-producing Klebsiella pneumonia (ATCC 700603) and Non- ESBL producing E. coli (ATCC 25922) were used as positive and negative control respectively. Statistical analysis
The summary and descriptive statistics were generated as percentages, proportions, mean and standard deviation. Dichotomous variables were compared using Pearson’s chi-square test or Fisher exact test as appropriate and continuous variables were compared using the Student’s t-test. To identify the association between patients characteristics and carriage of ESBL-producing Enterobacteriaceae, the univariate logistic regression was used. A p-value ≤ 0.05 was considered statistically significant. Effect sizes of associations of patients characteristics and ESBL-E carriage were reported using Odd ratios (OR) and 95% confidence intervals (CI). During logistic regression analysis, participants who had separated, divorced, widow and single marital status were combined to obtain single variable (unmarried) and was compared with married or cohabiting participants. History of admission prior to data collection was omitted from the model because all individuals with confirmed ESBL-E phenotypes (dependent variable) had no history of admission in the past three months. All statistical analyses were performed with STATA version 12 (Stata Corp., College station, Texas, USA).