Conclusion

38

CHAPTER FIVE

39 In a study of hospital acquired infections in Oshogbo, South-west Nigeria in 2011, three of seven enterococcal isolates (43%) isolated were found to be resistant to vancomycin²⁰. One of these VRE isolates was E. faecium and the rest E. faecalis. Infection control measures recommended to control spread of VRE include placing VRE infected or colonized patients in separate rooms from non-colonized patients, use of dedicated items like thermometers and sphygmomanometers for their care and use of gloves and gowns when attending to these patients, and ensuring proper hand hygiene after attending to them^5,14,71.

Rates of VRE fecal colonization reported elsewhere around the world include 37% in hematology patients in France⁷⁴, 10.9% in ICU, oncology, renal dialysis and burns unit patients in South Africa¹², and 2% among ICU patients and patients from the community in the Netherlands⁷⁶. It is difficult to compare the rate reported in this study to the above rates because of differences in the patient populations used. The patients surveyed in this study cut across medical, surgical and paediatric patients with varying degrees of disease severity whereas those studies were limited to specific patient groups. Moreover, while the majority of VRE found here were of vanC genotype, this genotype formed a small percentage of VRE in most other studies. Without vanC, the prevalence of VRE colonization in this study (vanA and vanB) would be 0.91%.

The low prevalence of VRE in this center could be explained by the low consumption of Vancomycin among patients. Only 2.43% of participants in this study had received Vancomycin. A meta-analysis of 20 epidemiologic studies showed that vancomycin exposure conferred a 4.5-fold increased risk of VRE acquisition⁸¹. However, there was high consumption of cephalosporins (65.96% of participants) and metronidazole (52.28% of participants) which have also been implicated in the acquisition of VRE⁸² but statistically

40 significant association was not established between use of these antibiotics and VRE colonization in this study. A review of the effects of antibiotics on the nosocomial epidemiology of VRE showed that prior administration of cephalosporins and metronidazole were independent risk factors for VRE acquisition⁸². This effect may be due to selective pressure which may allow enterococci including VRE to multiply and become detectable rather than causing direct mutation of the van genes.

The VRE found in this study included vanA (one), vanB (two) and vanC (eleven). VanA and vanB are acquired VRE resistance phenotypes which mediate high level glycopeptide resistance with MICs of 64->1000 mg/L for vanA and 4->1000 mg/L for vanB. VanA and vanB occur in E. faecium and E. faecalis. VanC phenotype is expressed constitutively in Enterococcus gallinarum, E. casseliflavus, and E. flavescens, and is characterized by low-level resistance to vancomycin with MICs of 2-32 mg/L. Others are vanD, vanE, vanG and vanL¹⁵ which are also acquired but occur less commonly in enterococcal isolates. vanA and vanB carrying enterococci are associated with severe infections that contribute significantly to mortality while vanC enterococci rarely cause severe infections. While most studies report more vanA than vanB, predominance of vanB over vanA was found in this study and has also been reported from South Africa¹² and Sweden⁸³.

Both vanB organisms recovered in this study had identical antibiogram and were recovered from two patients admitted in the same ward. This finding suggests that there may have been transmission of VRE between these patients although more definitive typing, for instance, Pulsed Field Gel Electrophoresis typing, was not done. VanB VRE have been shown to possess a high potential for nosocomial transmission and conjugal transfer^8,51,84.

41 The vanA and vanB isolates found in this study were E. faecium which accounts for most VRE strains, while the vanC isolates included ten E. gallinarum and one E. casseliflavus which are rarely associated with clinical infections. This is in line with other studies where most VRE found are E. faecium12,74,76,83

. The high number of vanC organisms recovered can be explained by the use of enrichment broth containing 6mg/L of vancomycin. Some studies have used broth containing higher concentrations of vancomycin excluding isolation of vanC enterococci. There are more than 20 species in the genus Enterococcus²⁸. E. faecalis and E.

faecium are the most prevalent pathogenic species accounting for more than 90% of clinical isolates³². Other enterococcal species which rarely cause human infection include E. avium, E. gallinarum, E. casseliflavus, E. durans, E. raffinosus and E. mundtii.

The MIC of vancomycin to the VRE strains were: >256mg/L for the vanA, 8mg/L for both vanB and 1-8mg/L for the vanC. Although these MICs were interpreted as “intermediate” or

“sensitive” for the vanB and vanC isolates using the breakpoints of the Clinical Laboratory Standards Institute (CLSI)⁶², these MICs are within the expected range for these VRE types, that is 4->1000 mg/L for vanB and 2-32 mg/L for vanC. Similar MICs for vanB and vanC have been reported in previous studies^76,80. The CLSI breakpoints have been set to exclude vanC phenotypes which have less significance for infection control purposes, meaning that some vanC carrying isolates have vancomycin MIC interpreted as sensitive.

All the vanA and vanB isolates were resistant to Ampicillin and Ciprofloxacin implying that these agents may not be useful if VRE infections occur. This pattern of resistance has also been found in other studies^11,56. High-level resistance to gentamicin occurred only in the vanB isolates and two vanC isolates. There are no studies found showing antimicrobial susceptibility patterns of VRE in Nigeria, however enterococcal isolates studied in Nigeria

42 have shown resistance rates of 42.8%²⁰ and 0%²¹ to Ampicillin and 42.8%²⁰, 64.4%⁴ and 51%²¹ to Ciprofloxacin. The rate of high-level resistance of enterococci to gentamicin was 9% in a study carried out in this institution²¹. All VRE isolates were susceptible to linezolid and this may be explained by the fact that linezolid has not been widely used in Nigeria.

Linezolid is a very attractive antimicrobial therapy for VRE infections due to its favorable pharmacokinetic distribution, low incidence of adverse effects, and oral bioavailability^85,86. VRE have also found to be uniformly susceptible to linezolid in other studies^35,83.

This study was only able to show significant association between VRE colonization and admission to the female medical ward. This association further buttresses the likelihood of nosocomial transmission of VRE in this hospital. Other potential risk factors tested were not associated with VRE colonization. They include participants‟ age, gender, duration of hospital stay, renal failure, surgery, malignancy, antineoplastic chemotherapy, antibiotic therapy, tuberculosis infection and diabetes. The absence of association of these factors with VRE colonization may however be partly due to the relatively small number of patients who were colonized with VRE as previous studies showed that prolonged length of stay and receipt of amikacin were risk factors associated with VRE acquisition among hematology-oncology patients in Chicago, USA³⁴. Other risk factors found in that study were prior hospitalization and previous ICU admission. Also, in a study of risk factors and mortality associated with vancomycin-resistant Enterococcus faecium infection and colonization at a tertiary care hospital in New York, USA, multivariate analyses found that duration of hospitalization greater than 7 days, intrahospital transfer between floors, use of vancomycin and third-generation cephalosporins, and vancomycin use for greater than 7 days were independently associated with VRE infection or colonization³⁶.

43 One limitation of this study was the small number of colonized participants which may have limited the detection of associations that may exist; perhaps larger studies in Nigeria may be able to detect possible associations between risk factors and VRE colonization.

44 CONCLUSION AND RECOMMENDATIONS

This study has shown that the prevalence of faecal colonization of patients on prolonged admission in LUTH is 4.26%. VanA gene was present in 7.14% of VRE, vanB in 14.29%, vanC2 in 7.14% while vanC1 was present in the remaining 71.43%. Of the VRE isolated, 92.8% were susceptible to Teicoplanin, 78.57% to Ampicillin, 21.43% to Ciprofloxacin, 100% to Linezolid while 28.57% displayed high level resistance to Gentamicin. Linezolid appears to be an effective agent for empirical treatment of VRE infections in Nigeria.

Although not yet widely available in Nigeria, this antimicrobial agent should be reserved for the treatment of serious VRE infections. Admission in a ward with VRE colonized patients is identified as a risk factor for VRE colonization reflecting the need for infection control.

The findings of this study reveal the presence of Vancomycin Resistant Enterococci (VRE) colonization and the potential for infection with VRE in the hospital studied highlighting the need for continuous surveillance and laboratory testing for Vancomycin resistance in enterococcal isolates for early identification of potential outbreaks of Vancomycin resistant enterococci infections and institution of control measures. The relatively low abundance of VRE gives opportunity to combat the emergence of VRE by instituting measures like antibiotic stewardship program and other infection control strategies.

Larger studies across other hospitals in the country are required to fully determine the extent of VRE colonization and infections in this country, as well as to determine the epidemiology and factors that may be responsible for the occurrence so as to guide policy to prevent further spread of these organisms. Also more resources need to be devoted to infection control

45 services in this hospital to prevent possible transmission of VRE from colonized patients to susceptible patients who may be admitted on the same wards.

46