Study population and demographics
To understand the demographics of the patient population, clients were characterised according to their sex and age group. Out of 4,617 patients who submitted samples for microbial analysis, 2246 (49%) were male and 2,371 (51%) were female (Figure 1). We observed that 88.3% (n =3889) were adult patients (>12 years old) while were 11.7% (n =517) were children (≤12 years old ) (Figure 1). Overall, more patients were registered in 2002 (626) and 2012 (618) but much less numbers were recorded in 2006 (130), 2008 (175) and 2014 (84) (Figure 2B).
Figure 1.Demographics of the study population. Patients were categorised by gender and age group.
Analysis of isolates by source of specimen and hospital department
To analyse the dynamics of bacterial infections, total number of specimens collected and isolates recovered were determined for each hospital department. Most samples were collected in the Out Patient Department (OPD;1,885, 43%; Figure 2A). Pus from wound and ear infections were the most frequent samples and the majority of them were collected in the OPD, male surgical ward, paediatric ward and female surgical ward (Figure 2A). Corresponding to the high number of samples collected, the OPD had the highest number of bacterial isolates (784, 44.5%; Figure 2A). TB ward had the least number of isolates (20, 1.1%). Across the departments, S. aureus was the most isolated pathogen (783, 43.5%) followed by Klebsiella species (387, 22%) (Figure 2B).
Figure 2. Distribution of isolates by specimen source and hospital department. Absolute number of (A) specimens and (B) isolates recovered per department were determined.
Prevalence of bacterial isolates
To evaluate the prevalence of bacteria pathogens over the study period, we determined the overall numbers of individual isolates and established the comprehensive figure of pathogens per year. Staphylococcus aureus was the most commonly isolated bacterium (783, 34.7%) (Figure 3A). Other common isolates included Klebsiella species (393, 17.4%), Proteus species (256, 11.4%), Coagulase-Negative Staphylococcus (193, 8.6%), Escherichia coli (169, 7.5%) and Pseudomonas species (131, 5.8%; Figure 3A). The pattern of the number of positive cultures matched the pattern of number of patients who submitted microbiology samples (Figure 3B). Altogether, the culture positivity rate was approximately 48.9% (2258/4611). Assuming that each patient submitted one sample, the highest culture positivity rate was recorded in 2011 (212/367; 57.7%) whereas the lowest rate was registered in 2005 (85/284; 29.9%; Figure 3C). In 2011, 54.2% (115/212) of the bacteria isolates were gram negative with Klebsiella species being dominant (25/115; 21.7%).
Figure 3. Prevalence of bacterial pathogens over the 13-year period.
(A) Shows the prevalence of isolates during the study period. (B) Describes the distribution of patients alongside positive cultures throughout the study period. (C) Demonstrate the culture positivity rates in different years of the investigation period.
Distribution of bacterial isolates according to demographics
To identify the most susceptible group from bacterial infections, isolates were distributed according to gender and age groups of the patients. The percentage of male and female patients whose samples were positive for bacterial culture was roughly the same i.e. 51% and 49% respectively (Figure 4A). A significant number of bacterial isolates were isolated from patients aged more than 12 years (Figure 4B). Largely, the distribution of isolates among male and females was fairly similar with prevalence rates of within 50% except for Pseudomonas species which were isolated more in males than females (63.1%, 36.9% respectively; Figure 4A). Most of the isolates were recovered from patients older than 12 years except S. pneumoniae which was isolated predominantly in clients younger than 12 years (88.2%; Figure 4B).
Figure 4. Prevalence of bacterial isolates per gender and age group
Isolated bacteria were distributed according to sex (A) and age group (B) of the patients.
Antimicrobial susceptibility profiles of major bacterial isolates
To assess antimicrobial susceptibility, most commonly isolated bacteria were tested for their susceptibility to the most commonly used antimicrobials at the hospital during the 13-year period. In comparison to other pathogens, S. pneumoniae demonstrated the highest rate of susceptibility to most of the antibiotics except for gentamicin where 40% of the strains showed resistance (Table 2). In this study, ciprofloxacin followed by gentamicin and cotrimoxazole proved to be the most effective antimicrobials with overall pathogen susceptibility rates of 84%, 75% and 70% respectively (Table 2). Nonetheless, worrying levels of antimicrobial resistance was registered in the study. On the whole, Pseudomonas species exhibited relatively the highest resistance to most antibiotics. Overall, high rates of antimicrobial resistance to erythromycin (49%), chloramphenicol (47%), and nalidixic acid (42%) were recorded (Table 1)
Table 2. Antimicrobial susceptibility patterns of major bacterial pathogens against commonly used antimicrobials during 2002-2014 period
The numbers in the table represent isolates found to be susceptible and resistant to the antimicrobials
Key: NA; Not Applicable, S; Susceptible R; Resistance