Understanding distribution of microbial pathogens and their associated infections is essential for controlling infectious diseases and monitoring of antimicrobial resistance. The current study aimed at establishing the prevalence of common pathogenic bacteria including their antimicrobial susceptibility patterns and distribution according to specimens, age groups and sex at Mzuzu Central hospital. We report a high prevalence of bacteria isolates with variability in susceptibility to key antimicrobials used during the study period. Most isolates displayed high resistance to erythromycin, gentamicin, chloramphenicol, nalidixic acid and cotrimoxazole. Conversely, majority of the isolates were sensitive to ciprofloxacin.
While a significant number of similar studies in Malawi were limited to investigating blood stream bacterial infections [5, 13-18], our study demonstrated the spread of bacterial infections where other body sites were surveyed (Figure 2A-B). The high prevalence of bacteria isolates observed in this study (Figure 3A) highlights the need for effective monitoring and surveillance of bacterial infections in resource-limited health care settings. There was a sharp decrease in number of isolates tested between 2003 and 2006 (Figure 3B), followed by a slow appreciation in subsequent years. Among other reasons, we suggest that this might have been as a result of reduced capacity of the laboratory to perform microbiology testing services. In 2004, the Malawi government had parted ways with a major donor supporting services at Mzuzu Central Hospital. Several services including laboratory services were negatively affected until a few years later when the government devised ways to fill the gap.
Similar to previous investigations [19-24], our findings revealed that S. aureus was the predominant cause of bacterial infections (Figure 3A). S. aureus is the common cause of skin and soft tissue infections [25, 26]. Hence it is not surprising that we observed considerably high number of isolates from OPD, male surgical ward and female surgical ward following culture of pus obtained from wound and surgical site infections. The subsequent prevalent pathogens in the study were Klebsiella and Proteus species (Figure 3A), which were also mostly recovered from wound pus. Likewise, this observation is comparable to investigations conducted in other countries [22, 23, 26-28].
The fluctuations in the number of patients that were provided with microbiology services correspond with the number of positive cultures. As the number of patients increased, positive cultures also increased and vice versa (Figure 3B). The relatively high bacterial culture positivity rates observed (Figure 3C) in this study could suggest good culture and bacterial isolation techniques. On the other hand, this could also be as a result of more contaminants being isolated, as most of the isolates i.e. S. aureus were isolated from pus, which can easily be contaminated with skin flora.
Except for S. pneumoniae most of the pathogens were isolated from patients >12 years old and adult patients (Figure 4B). The study registered more adults than children hence the observation that more isolates were recovered from adults corresponds with the high number of adult clients registered. S. pneumoniae is a common cause of bacterial meningitis in children , as such, our finding is consistent with literature. Correspondingly, our study showed that S. pneumoniae was predominantly isolated from CSF largely collected from children.
In general, all major isolates showed relatively high resistance to essential antimicrobials used during the study period (Table 2). Similar to previous studies [19, 30], our investigation showed higher rates of S. aureus resistance to chloramphenicol and erythromycin. Methicillin-resistant Staphylococcus aureus (MRSA) has significantly contributed to antimicrobial resistance globally , hence the drawback in this investigation is that S. aureus isolates were not tested to determine if some of the isolates were of MRSA origin.
S. pneumonia is a significant cause of pneumonia, sepsis, bacterial meningitis and death in Malawian children and adults [32-35]. Chloramphenicol is one of the antibiotics used in the treatment of bacterial meningitis including invasive pneumococcal diseases in Malawi. Previous investigations in Malawi reported higher rates of S. pneumoniae resistance to chloramphenicol which is in contrast to the findings in our study [5, 19]. Our observation needs to be interpreted with care since the number of isolates analysed in the current study is smaller than previous studies, hence, comparing the rates of antimicrobials resistance may not give a true reflection of the real situation. However, in general all major isolates exhibited high resistance to chloramphenicol.
The high rates of resistance to chloramphenicol, cotrimoxazole and nalidixic acid by major gram-negative organisms in the study is of concern as we observed a large population of patients affected during the study period. This is of importance as studies have shown an increased risk of subsequent infection and mortality after hospital discharge following colonisation with drug resistant gram-negative bacteria . Whilst drug resistant Gram-negative bacteria are recognised as a global problem in resource limited countries, the threat is much higher in areas with poor healthcare infrastructure and poor surveillance for antimicrobial resistance.
According to the Malawi Standard Treatment Guidelines, the antimicrobials used in the study are essential in the treatment of several conditions including sepsis, chronic diarrhoea and infant bacillary dysentery respectively . In addition, cotrimoxazole is used as a prophylactic treatment for bacterial infections in HIV positive clients in the WHO clinical stages II, III and IV . Overall, it is encouraging that ciprofloxacin proved to be relatively effective against most pathogens. In Malawi, ciprofloxacin is used in the treatment of bacillary dysentery in adults, sepsis, and also as a prophylactic treatment for meningococcal meningitis in adults .
Some of the limitations of this study include lack of patient history on previous antimicrobial use. Consequently, this might have an influence on the observed rate of antimicrobial resistance. Secondly, due to limited availability of raw data, we were not able to capture an in-depth analysis of critical epidemiological data such as name of referral hospitals for the patients, onset of disease, occupation, and HIV status. The study was conducted at one tertiary hospital in northern Malawi as such the findings cannot be generalized to the whole country. Lastly, laboratory data on pathogen isolation, identification and susceptibility testing was generated using conventional methods, hence the results may be limited. Nevertheless, this study has provided an awareness on common microorganism isolated in our set up, their distributions and antimicrobial resistance pattern. This data could help practitioners and policy makers to make informed decisions on management of patients