A Comprehensive review of abdominal infections

Abstract

Intra-abdominal infection (IAI) describes a diverse set of diseases. It is broadly defined as peritoneal inflammation in response to microorganisms, resulting in purulence in the peritoneal cavity[1]. IAI are classified as uncomplicated or complicated based on the extent of infection[2]. Uncomplicated abdominal infections involve intramural inflammation of the gastrointestinal (GI) tract without anatomic disruption. They are often simple to treat; however, when treatment is delayed or inappropriate, or the infection involves a more virulent nosocomial microbe, the risk of progression into a complicated abdominal infection becomes significant[3, 4]. Complicated abdominal infections extend beyond the source organ into the peritoneal space. They cause peritoneal inflammation, and are associated with localized or diffuse peritonitis[5]. Localized peritonitis often manifests as an abscess with tissue debris, bacteria, neutrophils, macrophages, and exudative fluid contained in a fibrous capsule. Diffuse peritonitis is categorized as primary, secondary or tertiary peritonitis. Primary peritonitis is also known as spontaneous bacterial peritonitis. It is thought to be the result of bacterial translocation across an intact gut wall[6]. These infections are commonly monomicrobial, and the infecting organism is primarily determined by patient demographics. For example, healthy young girls are most often infected by streptococcal organisms, cirrhotics by gram negative or enterococcal organisms, and peritoneal dialysis patients by Staphylococcus aureus[7, 8]. Diagnosis requires peritoneal fluid aspiration. Characteristics of infection include white blood cell count (WBC) > 500 cells/mm3, high lactate, and low glucose levels. Positive peritoneal fluid cultures are definitive, and resolution of infection is marked by peritoneal fluid with < 250 WBC/mm3[9]. Secondary peritonitis is caused by microbial contamination through a perforation, laceration, or necrotic segment of the GI tract[7]. Definitive diagnosis is based on clinical examination and history, and specific diagnoses can be confirmed by radiographic imaging[10]. If a patient is stable enough for transport, computed tomography (CT) scan with intravenous and oral contrast is the standard method of evaluating most intra-abdominal pathologies, such as appendicitis, diverticulitis, and colitis[11]. Suspected biliary pathology is the exception, and ultrasound is the preferred initial imaging modality for this spectrum of disease including acute cholecystitis, emphysematous cholecystitis, and cholangitis. Infections associated with secondary peritonitis are commonly polymicrobial and the infecting organisms are those most commonly associated with the source of contamination (see Table 1). Table 1 Expected organisms according to source Source Expected Organism Primary Peritonitis Young healthy female Streptococcus Cirrhotic Enteric gram negatives Enterococcus CAPD Staphylococcus aureus Secondary peritonitis Stomach and duodenum Streptococcus Lactobacillus Biliary E. coli, Klebsiella, Enterococcus Small Intestine E. coli, Klebsiella, Lactobacillus Streptococci Diptheroids Enterococci Distal ileum and colon Bacteroides fragilis Clostridium spp. E. coli Enterobacter spp. Klebsiella spp. Peptostreptococci Enterococci Teritiary peritonitis Enterococcus Candida Staphylococcus epidermidis Enterobacter Adapted from Weigelt JA [12]. Tertiary peritonitis represents an infection that is persistent or recurrent at least 48 hours after appropriate management of primary or secondary peritonitis. It is more common among critically ill or immunocompromised patients[12]. Because of the poor host defenses, it is also often associated with less virulent organisms, such as Enterococcus, Candida, Staphylococcus epidermidis, and Enterobacter[13]. Intra-abdominal sepsis is an IAI that results in severe sepsis or septic shock[2].