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Wound Infections in Two Health Institutions in Ile-Ife, Nigeria: Results of a Cohort Study
A wound is a breach in the skin, and exposure of subcutaneous tissue following loss of skin integrity provides a moist, warm, nutritive environment conducive to microbial colonization and proliferation.1 Wound contaminants may not persist, but species that grow and divide may become established, causing wound colonization or infection. The outcome depends on the interaction of complex host and microbial factors.2 Infection in a wound delays healing and may cause wound breakdown, herniation, or complete wound dehiscence.3
Despite technological advances in surgery and wound management, wound infection has been regarded as the most common nosocomial infection, especially in patients undergoing surgery.4 An important cause of illness, wound infection results in prolonged hospital stay and increased trauma care and treatment costs; in general, wound management practices become more resource demanding.1 The severity of complications depends largely on the infecting pathogen and site of infection.5,6 Usually, a wound can be considered infected if purulent material is observed, without the confirmation of a positive culture. The control of wound infections has become more challenging due to widespread bacterial resistance to antibiotics and to a greater incidence of infections caused by methicillin-resistant Staphylococcus aureus, polymicrobic flora, and fungi. Knowledge of the causative agents of wound infection, therefore, has proven to be helpful in the selection of empiric antimicrobial therapy and on infection control measures taken in health institutions.
This study investigated infected wounds of a patient cohort in two health institutions in Ile-Ife, Nigeria. Practitioners observed that treatment of wound infection was not guided by microbiological diagnosis, but they acknowledged that recognition of potential bacterial pathogens could assist wound care practitioners in the use of prophylactic and empiric antimicrobial therapy to aid in the prompt healing of wounds.
Material and Methods
Sample population. The prospective study included a cohort of 102 patients (70 men, 32 women, ages 2 to 72 years) presenting for wound dressing changes in the outpatient departments of the Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC) and the Health Centre, Ile-Ife, from July to December 1994. The wound types included boils, whitlow, abscesses, permicitis, trauma wounds, postoperative wounds, burns, systemic ulcers, insect bites, and swelling of unspecified etiology. Wound sites were categorized as follows: head and neck, back and abdomen, breast, armpit, arm, hand, thigh and groin, leg, and foot regions.
Sample collection. The initial step of wound management - including surgical debridement to remove necrotic and foreign materials in traumatic wounds and drainage of pus in boils, whitlow, abscesses, permicitis, inflammation, and insect bites - was conducted. Subsequent patient visits to health institutions for wound dressing changes indicated the presence of purulent discharge. Pus-producing wound types (postoperative, ulcers, burns) also were included in the study. Wounds were assessed as infected based on the presence of purulent discharge according to the criteria reported by Cutting and Harding.7 Before wound cleansing and dressing (performed by a nurse), an exudate sample was taken using sterile cotton-tipped applicators. Care was taken to avoid contamination by the normal skin flora. All cultures were transferred to the research laboratory and wound swabs from each site were immediately applied to freshly prepared blood agar plates, streaked, and incubated aerobically at 37 degrees C for 24 hours. Bacterial colonies on blood agar plates were later Gram stained. Characterization of bacterial isolates was based on standard microbiological methods,8 including Gram stain, morphological and cultural characteristics on nutrient agar, spore stain, motility and carbohydrate fermentation tests, nitrate reduction, catalase, hydrogen sulphide production, and indole production. Other tests include citrate utilization, gelatin liquefaction, Methyl Red-Voges Proskaeur test, coagulase, hemolysis on blood agar, morphological and cultural characteristics on mannitol salt, and eosin-methylene blue agar.
Results
Isolation of bacterial species. Of the 162 bacterial isolates recovered from various infected wounds (averaging 1.6 isolates per specimen), positive growth was observed in 95% of wound cultures. One micro-organism was present in 39 wound cultures, several micro-organisms in 55 cultures, and no bacterial isolate was obtained from the cultured material in eight cultures. Eleven bacterial genera and 17 species were identified (see Table 1). Staphylococcus aureus was the most frequently isolated microorganism (25%), followed by Escherichia coli (12%), Pseudomonas aeruginosa (9%), and Staphylococcus epidermidis (9%). Staphylococci were the predominant Gram-positive organism (41%) and the family Enterobacteriaceae constituted 37% of isolates. Bacterial isolates identified as Klebsiella pneumoniae, Enterobacter cloacae, Proteus spp and Pseudomonas spp accounted for less than 7% of the isolates.
Forty percent (40%) of wounds were caused by trauma, and 42% of isolates were recovered from this wound type (see Table 2). Fifteen bacterial species were identified from trauma wounds, followed by boils (10) and abscess (9), respectively. Sixty-three isolates (63, 39%) were obtained from wound types that required incision and drainage (I + D) to remove the exudate and clean the underlying tissue (incised boils, whitlows, abscesses, and permicitis). S. aureus was the predominant micro-organism, constituting 31% of the isolates recovered from these wound types. The analysis of polymicrobial infections showed that 31 out of 55 (56.3%) polymicrobial cultures were attributed to S. aureus with other micro-organisms. They include 10 cases of S. aureus with Gram-positive organisms, 19 cases of S. aureus with Gram-negative organisms, and two cases involving S. aureus, Staphylococcus spp, and a Gram-negative organism. Nine cases of polymicrobic infections involving Bacillus spp, and Gram-negative organisms were recorded from a variety of wound types.
The location of wounds in relation to wound types and organisms isolated from each wound site is shown in Table 2. Trauma wounds were mainly located at the leg and foot regions. Wound infection at the extremities was observed in 27 cases in the hand and leg regions, followed by 19 cases on the foot, and 15 cases in the thigh and groin regions of the body. S. aureus was recovered from all the wound sites except the arm; it was the most frequently isolated micro-organism in wounds occurring in all the regions of the body, excluding the hand and leg.
Discussion
Wound infection is a major concern among healthcare practitioners, not only in terms of increased trauma to the patient but also in view of its burden on financial resources and the increasing requirement for cost-effective management within the healthcare system.1 Microbiological analysis reveals that S. aureus is the leading etiologic agent of wound infection in these health institutions. This is similar to reports in Nigeria, India, Thailand, and Japan.9-12 S. aureus was the most frequently isolated micro-organism from wounds caused by incision to reach pus or fluid collection under the skin surface, as well as from various wound types in this study. Microbiological investigations have noted that this organism is the single causative bacterium in approximately 25% to 69% of cutaneous abscesses.13-15 The same micro-organism also has been recognized as the most frequent isolate in superficial infections seen in hospital accident and emergency departments.15 The presence of S. aureus nasal carriage has been identified as an important risk factor for the acquisition of S. aureus infection, although this may depend on an array of factors that may either be environmental or patient-related.16 The postulated sequence of events leading to infection is initiated with S. aureus nasal carriage, which is then disseminated via the hands to other body sites where infection can occur through breaks in the dermal surfaces.17
A multivariate logistic regression analysis of superficial abscesses attributed to S. aureus conducted in Khartoum, Sudan, revealed that a history of abscess, recent traditional medical treatment, poor hygiene, and low socio-economic status were significantly and independently associated with the occurrence of superficial abscesses.16 Analysis on the impact of personal hygiene was not conducted in this study but suggest that basic standards of patient hygiene could be an important subject of education in the basic healthcare system in developing countries. Nurses in charge of outpatient departments generally administered penicillin G powder to the wound site during wound dressing as a way of curtailing infection. Unfortunately, no patient follow-up occurred to assess the effectiveness of wound care management in these hospitals on wound healing. In a related study, S. aureus strains isolated from septic wounds of patients in these health institutions during the same period were resistant to penicillin G (data not shown), with a high proportion of strains demonstrating resistance to commonly used antibiotics.18 The study suggested that the practice of administering penicillin G during dressing on wound sites should be discouraged. The procedure could contribute to wound healing delay, prolonged course of infection, and the emergence of antibiotic-resistant bacteria.
The number of trauma wound infections observed in the current study was high (40%). The wounding agents ranged from nail pricks from farm equipment to door slams on fingers and motorcycle accidents. Trauma is often associated with the development of local or systemic infection, and the situation in which injury or trauma occur, as well as the location of the injury, may be predictive of the number and types of pathogens found in the wound. Infecting micro-organisms may be derived either from an exogenous source (ie, water-borne from water-related injury or micro-organisms from soil in a soil-contaminated injury) or the endogenous microflora of the patient.19 Fifteen bacterial species were identified and 42% of the total number of isolates was recovered from trauma wound infection. A high number of traumatic wound infections were located on the leg and foot regions of the body - ie, the extremities.
Traumatic wound infection of the extremities is a common clinical problem. The high frequency and variety of micro-organisms confirms the view that microbiological evaluation before treatment should be strictly observed.20 General principles of infection prevention following severe trauma include aggressive, intensive care to maintain blood volume and support respiratory function and nutrition. Prompt drainage of collecting fluid, evacuation of hematoma, and debridement of devitalized tissues optimizes outcome. Prompt infection control measures, such as hand washing and the wearing of gloves by wound care practitioners, could reduce the spread of potential pathogens and the risk of infection by resistant bacteria.21
The relationship between colonization and infection was not investigated. Nevertheless, evidence shows that delayed healing in a chronic wound that has no signs of clinical infection, suggestive of critical colonization, is directly related to the microbial microburden, notably hemolytic Streptococci and anaerobes.22 Early and appropriate intervention can avoid progression to critical colonization and infection; thus, potentially improving healing rates and reducing the risk of cross-infection.23
Antiseptics and disinfectants have long been the cornerstone of effective infection control and the prevention of hospital-acquired infection. Wounds most likely to benefit from topical antiseptic treatment are primarily traumatic or chronic in nature, heavily contaminated with a variety of micro-organisms, and/or failing to heal, with or without clinical signs of infection.1 The use of topical silver and iodine-containing release formulations on infected and critically colonized wounds can, as part of an holistic approach, be supported. Such practices also help reduce odor and local bioburden, lowering the risk of cross-infection.22 While odor control alone does not eradicate infection or alter bacterial growth, it offers substantial patient quality-of-life benefits and, therefore, should be an adjunct to any topical and or systemic antibacterial therapy.24
Antimicrobial agents (antibiotics) are primarily used either prophylactically in the treatment of wounds that are likely to be heavily contaminated following surgery or therapeutically in the treatment of clinically infected wounds. Because both aerobic and anaerobic pathogens may contribute to infection in polymicrobial wounds, broad-spectrum antibiotics provide the most successful treatment. In addition, wound cleansing and surgical debridement may assist antibiotic treatment by reducing the microbial load, enabling better penetration of antibiotics. Delayed wound closure also may be considered to allow time for antimicrobial therapy to reduce the microbial load.1 Additionally, other treatment options, such as hyperbaric oxygen therapy (HBO), antimicrobial peptides, and botanical extracts may play a role in wound management and are worthy of consideration.
Conclusion
Most wound infections in these health institutions were polymicrobial in nature and, in most cases, associated with S. aureus and other micro-organisms. The variety of organisms observed in this study support the need to obtain culture specimens from infected wounds for microbiological evaluation and antibiotic susceptibility determination so adapted chemotherapy can be prescribed. The authors believe this will not only facilitate successful wound management, but also assist in the control of antibiotic usage; hence, stemming the spread of antibiotic-resistant bacteria. The fact that surgical incisions and wound debridement may delay wound healing underscores the fact that information regarding site, type of wound infection, and clinical symptoms should be considered along with the value of identifying one or more bacterial pathogens. Infection control measures, such as wound care clinicians washing hands and wearing gloves, could reduce the spread and risk of infection by resistant bacteria. Continuous dialogue between the microbiology department and wound care practitioners is strongly advised in keeping with saving cost and time and providing prompt and appropriate treatment.
Further investigation is needed to understand: a) the epidemiology of wound infection, especially in community acquired infection, b) the impact of the patient's level of hygiene on the occurrence of superficial abscesses, c) the relationship between colonization and infection, and d) antimicrobial susceptibility patterns of pathogens associated with wound infection. Studies on the effect of alternative antimicrobial therapies on wound infection and wound healing also should be encouraged.
Acknowledgements
The authors are grateful to the nurses of the Outpatient Department of the Obafemi Awolowo University Teaching Hospitals Complex for their assistance in the specimen collection. The project was partly supported by grant 1425 LF, awarded by the Obafemi Awolowo University Research Committee. The authors thank Bongi Sigwebela (University of Zululand) for assistance in the acquisition of research articles.
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