Microbiological patterns of bacterial bloodstream infections and predictors of kidney dysfunction at a tertiary hospital in Zambia

¹Department of Cardiovascular Science and Metabolic Diseases, Livingstone Center for Prevention and Translational Science, Livingstone, Zambia, ²Department of Pathology, Ndola Teaching Hospital, Ndola, Zambia, ³Department of Biomedical Sciences, Chikankata College of Biomedical Sciences, Mazabuka, Zambia, ⁴Department of Biomedical Sciences, Ndola College of Biomedical Sciences, Ndola, Zambia

^&Corresponding author
John Nzobokela, Department of Cardiovascular Science and Metabolic Diseases, Livingstone Center for Prevention and Translational Science, Livingstone, Zambia

Introduction    

Bloodstream infections (BSIs) remain a major cause of morbidity and mortality globally, with a disproportionately high burden in low- and middle-income countries [1,2]. A critical but often under-recognized complication of BSIs is kidney dysfunction, which is associated with prolonged hospitalization, increased need for intensive care, and higher mortality rates [3].

The clinical impact of BSIs is further worsened by the rise of multi-drug-resistant (MDR) organisms [4]. Evidence from upper-middle-income countries in Africa and the Western Pacific indicates that pathogens such as Enterobacteriaceae, Acinetobacter baumannii, and Staphylococcus aureus are commonly implicated in severe BSIs and are linked to adverse clinical outcomes [1,2].

In sub-Saharan Africa, the true burden of BSI-related kidney dysfunction is likely underestimated because of limited access to blood culture diagnostics and inconsistent renal monitoring [5]. However, routinely available laboratory markers may offer practical tools for early risk stratification in resource-limited settings.

In Zambia, data on the prevalence of kidney dysfunction among patients with BSI, its predictors, and the spectrum of causative organisms remain scarce. This study therefore aimed to determine the prevalence of kidney dysfunction in patients with bloodstream infections, identify its clinical and laboratory predictors, and describe the microbiological profile of bloodstream isolates at Ndola Teaching Hospital (NTH) in Zambia.

Methods     

Study design and setting: this was a laboratory-based, single-center retrospective cohort study conducted at NTH, a tertiary referral hospital in Ndola, Copperbelt Province, Zambia. NTH is a major referral center for specialized medical care and serves an average of 29,485 patient admissions per year, providing comprehensive clinical and diagnostic services, including microbiology and renal function testing.

The study reviewed data from patients with confirmed bloodstream infections diagnosed between January and December 2025. Data extraction was conducted after ethical approval, from 1^st November, 2025 to 10^th January, 2026, using records retrieved from the laboratory information system (LIS)-DISA database.

Study participants and eligibility: the study included adult patients (≥18 years) with at least one laboratory-confirmed bloodstream infection and documented renal function results (serum creatinine and/or estimated glomerular filtration rate) at the time of hospital admission. Patients were excluded if they had incomplete or missing laboratory records, duplicate blood culture isolates from the same infectious episode, or organisms classified as contaminants. Contaminants were defined according to Clinical and Laboratory Standards Institute (CLSI) guidelines, including common skin commensals (e.g., coagulase-negative staphylococci, Corynebacterium spp., Bacillus spp., and Micrococcus spp.) isolated from a single blood culture without clinical evidence of infection, or organisms inconsistent with the patient´s clinical presentation. Additionally, patients with sickle cell disease or malignancies that could affect complete blood count parameters were excluded to avoid confounding of hematological predictors of kidney dysfunction.

Population: all 582 positive blood culture entries on the DISA*Lab were reviewed. After excluding incomplete records, duplicate isolates, contaminants, and patients with sickle cell disease or malignancies, 232 participants with confirmed bloodstream infections were included.

Study variables: the primary outcome of this study was kidney dysfunction, defined as an estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m² at hospital admission. Independent variables included demographic factors age (categorized into three clinically meaningful groups: 18-39 years, 40-59 years, and ≥60 years, reflecting increasing risk of kidney dysfunction with advancing age and consistent with prior studies on infection-related renal impairment [6,7]) and sex, clinical factors (care unit at the time of bloodstream infection), laboratory parameters (hemoglobin, platelets (PLT), red cell distribution width (RDW), white blood cells (WBC)). Absolute neutrophil, lymphocyte, and monocyte counts, as well as calculated inflammatory ratios such as hemoglobin-to-red cell distribution width ratio (HB/RDW), derived neutrophil-to-lymphocyte ratio (dNLR), neutrophil-to-platelet ratio (NPR), and systemic immune-inflammation index (SII), common comorbidities included hypertension, diabetes mellitus, HIV infection and pre-existing chronic kidney dysfunction (CKD), defined as a documented history of CKD prior to the current hospital admission, based on prior medical records and clinician diagnosis and microbiological factors such as; type of bloodstream isolate, including gram-negative versus gram-positive bacteria, Enterobacterales, non-fermentative bacteria, and multidrug-resistant organisms. These variables were evaluated to determine predictors of kidney dysfunction and to describe the microbiological profile of bloodstream infections in the study population.

Data analysis: data were collected, cleaned, coded, and analyzed using Stata version 15. Descriptive statistics, including proportions, frequencies, medians, and interquartile ranges (IQR), were used to summarize study variables. The Shapiro-Wilk test was applied to assess the normality of continuous variables. Associations between kidney dysfunction and independent variables were evaluated using bivariate analysis, and variables with p<0.05 were included in a multivariate logistic regression model to identify independent predictors. Results were reported as odds ratios (OR) with 95% confidence intervals (CI), with statistical significance set at p<0.05.

Ethical considerations: ethical approval was obtained from the Mulungushi University School of Medicine and Health Sciences Research Ethics Committee (IRB: 00012281, FWA: 0002888, Ref. No.: SMHS-MU1-2025-37) on 17^th March, 2025, and the National Health Research Ethics Board (REF: NHRA-2246/20/05/2025) on 5^th June, 2025. Authorization to conduct the study was granted by Ndola Teaching Hospital. All data were de-identified to ensure confidentiality, and no information that could identify participants was collected. Written or verbal consent was waived by the ethics committees. The study was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice guidelines.

Results     

Descriptive and microbiological characteristics: a total of 232 patients with laboratory-confirmed bloodstream infection were included in the study. The largest proportion of participants were aged 18-39 years (37.9%), followed by those aged ≥60 years (34.9%), and 27.2% were between 40-59 years. Females constituted 51.3% of the cohort, while males made up 48.7%. Kidney dysfunction at admission was present in 58.6% (136/232) of patients, whereas 41.4% (96/232) had no evidence of renal impairment. Hospital location at the time of bloodstream infection refers to the ward or unit where the patient was physically admitted when the blood culture was collected, reflecting the setting in which infection was first suspected and evaluated. Among the participants, 50.4% of patients were in the general wards, 37.5% in the emergency/admission unit, and 12.1% in the intensive care unit. Regarding comorbidities, hypertension was present in 11.2% (26/232) of patients, diabetes mellitus in 4.3% (10/232), pre-existing chronic kidney disease in 27.2% (63/232), and HIV infection in 15.9% (37/232). Gram-negative bacteria accounted for 67.1% of all bloodstream isolates, with Enterobacterales comprising 52.2% of total pathogens. The most frequent Enterobacterales were Enterobacter agglomerans (15.1%), Klebsiella pneumonia (10.8%), and Escherichia coli (8.2%). Non-fermentative gram-negative organisms represented 15.5% of isolates, predominantly Acinetobacter baumannii (8.6%) and Pseudomonas spp. (6.0%). Gram-positive bacteria constituted 32.3% of isolates, led by Staphylococcus aureus (16.8%), followed by Streptococcus pneumonia (6.5%) and Enterococcus faecalis (4.3%). Multidrug-resistant organisms (MDROs) were identified in 58.2% of isolates, while 41.8% were non-MDRO pathogens (Table 1).

Relation between kidney dysfunction and clinical and laboratory characteristics: patients with kidney dysfunction were significantly older than those without renal impairment (p<0.001). The prevalence of kidney dysfunction was lowest among individuals aged 18-39 years (26.5%), slightly higher in those aged 40-59 years (27.9%), and highest in patients aged ≥60 years (45.6%). Among comorbidities, hypertension (17.6% vs. 2.1%, p<0.001) and pre-existing chronic kidney disease (45.6% vs. 1%, p<0.001) were significantly more frequent in patients with kidney dysfunction (Table 2).

With respect to hematological parameters, median HB levels were significantly lower in patients with kidney dysfunction at admission (8.3 (6.3-11.1) g/dL) compared with those without renal impairment (10.1 (7.7-13.1) g/dL) (p < 0.001). RDW was higher in the kidney dysfunction group (16.4 (14.9-19.7)) than in patients without kidney dysfunction (14.9 (13.6-18.1)) (p = 0.002), resulting in a significantly lower HB/RDW ratio (0.50 (0.32-0.69) vs. 0.66 (0.45-0.94), p<0.001). Platelet counts were reduced in patients with kidney dysfunction (139 (81.2-266) x10⁹/L) compared with those without kidney dysfunction (189 (102-297) x10⁹/L) (p = 0.012). Additionally, patients with kidney dysfunction had higher absolute neutrophil counts (ANC) (7.24 (3.90-14.5) x10⁹/L vs. 5.84 (3.21-9.43) x10⁹/L, p = 0.009), derived neutrophil-to-lymphocyte ratio (dNLR) (4.44 (2.36-8.34) vs. 2.99 (1.88-5.10), p = 0.005), and neutrophil-to-platelet ratio (NPR) (0.05 (0.02-0.09) vs. 0.03 (0.01-0.06), p = 0.001) than those without kidney dysfunction (Table 3).

Predictors associated with kidney dysfunction in logistic regression: in unadjusted logistic regression analysis, older age, lower HB, lower platelet counts, higher ANC, higher WCC, and lower HB/RDW were associated with increased odds of kidney dysfunction. Patients aged 40-59 years had more than twice the odds of kidney dysfunction compared with those aged 18-39 years (OR 2.19; 95% CI 1.13-4.24; p = 0.015), while those aged ≥60 years had nearly fivefold higher odds (OR 4.71; 95% CI 2.41-9.18; p < 0.009). Pre-existing CKD was also strongly associated with kidney dysfunction in univariable analysis (p<0.001).

After adjustment for potential confounders, older age remained an independent predictor of kidney dysfunction. Compared with patients aged 18-39 years, those aged 40-59 years had 2.39-fold higher odds (AOR 2.39; 95% CI 1.01-5.61; p = 0.045), and patients aged ≥60 years had more than fivefold higher odds (AOR 5.62; 95% CI 2.41-13.08; p<0.001). Pre-existing CKD remained strongly associated with kidney dysfunction (AOR 0.007; 95% CI 0.00-0.11; p<0.001).

Among laboratory markers, a lower HB/RDW ratio independently predicted kidney dysfunction (AOR 0.04; 95% CI 0.03-0.85; p = 0.039), while lower platelet counts were also significant (AOR 0.995; 95% CI 0.994-0.998; p = 0.02). Other variables, including sex, hypertension, WCC, HB, ANC, and NPR, were not independently associated with kidney dysfunction after adjustment (Table 4).

Criteria for determination of multidrug-resistant organism status: multidrug-resistant organism (MDRO) status was determined based on phenotypic antimicrobial susceptibility testing results. An isolate was classified as MDRO if it showed non-susceptibility (resistant or intermediate) to at least one antimicrobial agent in three or more distinct antimicrobial classes. Resistance was assessed across the following major antimicrobial classes, depending on organism type (Table 5).

Discussion     

This study demonstrates a high prevalence of kidney dysfunction (58.6%) among adults with bloodstream infections at Ndola Teaching Hospital, highlighting the substantial renal burden associated with BSI in a tertiary care setting. Gram-negative bacteria predominated, particularly Enterobacterales such as Enterobacter agglomerans, Klebsiella pneumonia, and Escherichia coli, which are clinically significant due to their frequent association with severe infections, healthcare-associated transmission, and multidrug resistance [8,9]. Gram-positive organisms, led by Staphylococcus aureus, also contributed substantially, with multidrug-resistant organisms comprising over half of all isolates, reflecting the growing challenge of antimicrobial resistance.

The high prevalence of kidney dysfunction aligns with previous reports where infection and sepsis are major contributors to acute kidney injury, with incidence estimates ranging from approximately 14% to over 60% depending on patient populations and definitions [10]. This underscores the substantial burden of renal involvement in systemic infections and highlights the importance of early renal monitoring [11].

The microbiological profile in this study, where gram-negative bacteria accounted for 67.1% of bloodstream isolates, with Enterobacterales predominating and non-fermentative organisms such as Acinetobacter baumannii and Pseudomonas spp. also frequently isolated, alongside gram-positive pathogens led by Staphylococcus aureus, is consistent with findings from other settings. In a large surveillance study reported that gram-negative organisms comprised approximately two-thirds of bloodstream infection isolates, with Escherichia coli, Klebsiella pneumonia, and non-fermenters among the most common pathogens, while S. aureus remained a leading gram-positive cause of BSI [12]. Similarly, a retrospective cohort of multidrug-resistant bloodstream infections found that gram-negative bacteria such as E. coli, K. pneumoniae, Pseudomonas spp., and Acinetobacter spp. were the predominant isolates, with S. aureus also frequently recovered [13]. In a study from The Gambia, S. aureus and Klebsiella spp. were the most common bloodstream pathogens, with other Enterobacterales and non-fermentative organisms also present [14]. A similar distribution was observed in an Indian multicenter study where gram-negative bacilli, including E. coli, K. pneumoniae, Pseudomonas aeruginosa, and Acinetobacter spp. accounted for a majority of BSI isolates [15]. These corroborative studies from diverse geographic regions underscore the global predominance of gram-negative bacteria in BSIs and the persistent role of key pathogens such as Enterobacterales, A. baumannii, Pseudomonas spp. , and S. aureus in bloodstream infection epidemiology. A recent systematic review and meta-analysis including studies from Africa and other low- and middle-income settings consistently identified Escherichia coli, Klebsiella spp., and Staphylococcus aureus as the leading causes of bacteremia, with high levels of resistance to third-generation cephalosporins and other commonly used antibiotics, underscoring their importance as priority pathogens for antimicrobial resistance surveillance and empiric therapy planning [16,17].

In multivariable analysis, older age was a strong independent predictor of kidney dysfunction at admission. Participants aged 40-59 years and ≥60 years had significantly higher odds of renal impairment compared with those aged 18-39 years. This is consistent with evidence that the likelihood of developing acute kidney injury increases with age, as age-related structural and functional renal decline and a higher burden of comorbidities predispose older adults to renal impairment in critical illness and sepsis [18]. A recent cohort study has shown that advancing age is independently associated with higher acute kidney injury (AKI) risk in critically ill and septic populations, with a stepwise increase in AKI incidence and kidney dysfunction among older age groups [19]. In our study, AKI was considered within this broader clinical context but was not directly diagnosed. Pre-existing chronic kidney disease at admission was also associated with kidney dysfunction compared with patients without a history of chronic kidney disease in our study. Prior studies similarly identify baseline chronic kidney disease as a major risk factor for poor renal outcomes during systemic infections and critical illness, reflecting reduced physiological reserve and susceptibility to further injury in patients with sepsis [20-22].

Among hematological markers, a lower HB/RDW ratio was independently associated with kidney dysfunction. Elevated RDW and related red cell distribution metrics have been linked with kidney dysfunction incidence and severity in critically ill or septic patients in multiple studies, suggesting that anisocytosis and erythrocyte turnover reflect systemic inflammation and impaired microvascular function in renal injury [22]. Similarly, lower platelet counts independently predicted kidney dysfunction. Thrombocytopenia has been reported as a predictor of kidney dysfunction in sepsis and HIV-associated sepsis cohorts, with lower platelet counts marking more severe systemic inflammation, endothelial dysfunction, and greater renal vulnerability [23]. In a prospective cohort of sepsis patients in Uganda, thrombocytopenia was independently associated with the development of kidney dysfunction [24]. In critically ill kidney dysfunction patients, reductions in platelet count have been correlated with greater adverse renal events and worse outcomes, including increased risk of major adverse kidney events and mortality [25].

While the precise mechanisms underlying kidney dysfunction in bloodstream infection remain complex and multifactorial, our findings highlight that both host factors (older age, chronic kidney disease at index admission) and readily available laboratory markers (HB/RDW ratio, platelet count) can help identify patients at high risk of renal impairment. However, due to the retrospective design and reliance on single-time-point serum creatinine measurements at admission, we were unable to reliably distinguish between acute kidney injury and chronic kidney disease. Consequently, the outcome in this study is best interpreted as kidney dysfunction at admission, with acute and chronic renal impairment considered possible underlying contributors rather than confirmed diagnoses. Prospective studies incorporating longitudinal kidney function assessments and biomarkers of early renal injury are needed to better delineate these pathways in patients with bloodstream infections.

Strengths and limitations: this study has several limitations. Its retrospective, single-center design may limit generalizability and is subject to incomplete or missing clinical records, which could have affected the accuracy of some variables. In addition, although the sample size was adequate to detect major associations, it may have limited statistical power to identify more subtle predictors. Despite these limitations, the study has important strengths. To our knowledge, this is the first study in the region to comprehensively examine the relationship between bloodstream infections and kidney dysfunction, providing novel and locally relevant evidence. The use of the DISA*Lab laboratory information system enabled robust capture of high-quality microbiological and hematological data, strengthening the reliability of our findings. Importantly, this study provides real-world evidence from a resource-limited setting, which is directly applicable to routine clinical practice. Our findings have potential to inform service delivery, guide early risk stratification, and support policy decisions related to the management of patients with kidney dysfunction and infections caused by multidrug-resistant organisms in similar settings.

Conclusion     

Kidney dysfunction at admission was highly prevalent among adults with bloodstream infections at Ndola Teaching Hospital, affecting nearly six in ten patients. Independent predictors included older age, pre-existing chronic kidney disease, lower hemoglobin-to-RDW ratio, and thrombocytopenia, highlighting patients at greatest risk. Gram-negative bacteria, particularly Enterobacterales, and multidrug-resistant organisms predominated among bloodstream isolates. These findings emphasize the need for early renal assessment, close monitoring of high-risk patients, and strengthened infection control and antimicrobial stewardship to reduce the burden of renal complications in resource-limited settings.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Conceptualization, data curation, formal analysis, investigation, methodology, resources, writing - original draft: John Nzobokela; methodology, visualization, writing - review and editing: David Chisompola; visualisation, writing - review and editing: Elijah Chinyante and Lucky Kalyapu; validation, writing - review and editing: Luswepo Namwinga; supervision, methodology, validation, data analysis, writing - review and editing: Nanjela Chindima. All the authors read and approved the final version of this manuscript.

Acknowledgments     

The authors would like to thank Ndola Teaching Hospital management for granting permission to conduct the study at the Department of Pathology.

Tables     

Table 1: demographic characteristics, clinical features, and microbiological profile of bloodstream infection isolates among adult patients with laboratory-confirmed bloodstream infections at Ndola Teaching Hospital, Ndola, Zambia, January-December 2025 (N = 232)

Table 2: association between kidney dysfunction and clinical characteristics among adults with laboratory-confirmed bloodstream infections (N = 232)

Table 3: association between kidney dysfunction and laboratory characteristics among adults with laboratory-confirmed bloodstream infections (N = 232)

Table 4: predictors associated with kidney dysfunction in logistic regression

Table 5: operational definition and criteria used to determine multidrug-resistant organism (MDRO) status among bacterial bloodstream isolates

References