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Neisseria Meningitidis Infections

Definition Neisseria meningitidis (the meningococcus) is the cause of epidemic bacterial meningitis, fulminant sepsis (meningococcemia), milder bacteremia, and, less commonly, focal infections (such as pneumonia, septic arthritis, purulent pericarditis, urethritis, and conjunctivitis). The Pathogen N. meningitidis is an aerobic, diplococcal gram-negative β-proteobacterium and a member of the family Neisseriaceae, which also includes Neisseria gonorrhoeae ( Chapter 275 ), the cause of gonorrhea. The meningococcus is a…

Diseases Caused by Non–Spore-Forming Anaerobic Bacteria

Definition Anaerobic bacteria are the predominant members of the indigenous microbiota, including the skin and the oral, gastrointestinal, and vaginal mucosa ( Fig. 273-1 ; Table 273-1 ). However, the types of predominant anaerobes differ by location. TABLE 273-1 LOCATION OF VARIOUS GROUPS OF ANAEROBES AS NORMAL MICROFLORA IN HUMANS NO. OF ORGANISMS PER GRAM LOCATION AEROBES ANAEROBES PREDOMINANT ANAEROBIC BACTERIA Skin — — Cutibacterium acnes…

Gram-Positive Rod Infections

Infections Caused by Bacillus Anthracis and Other Bacillus Species Definition The genus Bacillus includes several species that are closely related phylogenetically. The Bacillus cereus group includes Bacillus anthracis , which is the causative agent of anthrax; Bacillus cereus , which causes food poisoning as well as localized and systemic infections; and Bacillus thuringiensis , an insect pathogen that causes eye infections and infections in immunocompromised persons.…

Clostridial and Clostridioides Infections

Diarrheal Syndromes Clostridioides Difficile Infection Definition The hallmark of C. difficile infection is diarrhea, most commonly during or after (up to 3 months) a course of antibiotics. Most cases are defined by the presence of clinically significant diarrhea (three or more loose or unformed bowel movements per day) plus evidence of toxigenic C. difficile or its toxins A and/or B in stool. C. difficile infection can…

Enterococcal Infections

Definition Enterococci are endogenous human gut flora that are increasingly important health care–associated pathogens. Enterococci cause urinary tract infections, bacteremia, intra-abdominal infections, and, rarely, endocarditis and meningitis. Their emergence as major pathogens results from their inherent resistance to commonly used antimicrobial agents, persistence in the environment, association with indwelling devices, and transmission from patient to patient, mostly by way of the contaminated hands of health care…

Nonpneumococcal Streptococcal Infections and Rheumatic Fever

Classification and Identification of Streptococci Streptococci are gram-positive facultatively anaerobic, catalase-negative coccoid bacteria that grow in chains and colonize the skin and mucous membranes. When grown on blood agar plates, they may cause complete (β), incomplete (α), or no (γ) hemolysis. Using the Lancefield classification, hemolytic streptococci can be classified into types A through G based on acid-extractable carbohydrate antigens of cell wall material. Modern classification…

Streptococcus Pneumoniae Pulmonary Infections

Definition Streptococcus pneumoniae ( S. pneumoniae ) is a significant human bacterial pathogen and a major cause of community-associated bacterial infections. It is the most common bacterial cause of community acquired pneumonia (pneumococcal pneumonia; Chapter 85 ), sinusitis ( Chapter 394 ), and bacterial meningitis ( Chapter 381 ). Despite the availability of an effective vaccine, the burden of pneumococcal pneumonia remains high, particularly in older…

Staphylococcal Infections

Definition Staphylococci are well adapted as commensals and as pathogens. Coagulase-negative species constitute a significant proportion of the normal human cutaneous microbiome. Staphylococcus aureus , a coagulase-positive species, is a nasopharyngeal colonizer in a third of individuals, most of whom will not become infected. As a pathogen, S. aureus infections range in severity from relatively trivial skin infections to lethal invasive disease. Coagulase-negative species, which are…

Antibacterial Chemotherapy

Antibiotics provide a backbone for modern interventional medicine, in which surgery, central venous catheters, urinary catheters, implantable devices, and mechanical ventilation have become commonplace. These interventions support seriously ill patients, but they also give bacteria access to normally sterile areas. Therapies for cancer and immune-mediated disease often leave patients severely immunosuppressed. Bacterial infections in such patients are serious, and antibiotics provide critical life-saving support for such…

Approach to the Patient Before and After Travel

Prevention strategies and medical interventions for travelers should be individualized according to a risk assessment that considers both the itinerary and factors that are dependent on the prospective traveler. A structured approach to patient interaction ( Table 265-1 ) is the most efficient way to cover the necessary educational and preventive interventions. Providing clearly printed instructions in lay language is advised. The worldwide epidemiology of travel-related…

Approach to the Patient with a Sexually Transmitted Infection

Sexually Transmitted Infections Definition Sexually transmitted infections (STIs) include a wide variety of organisms that are transmitted through intimate contact involving skin or mucosal surfaces of the oropharynx, vagina, penis, and rectum. STIs can generally be divided into five broad categories (syndromes): urethritis, genital ulcers, epithelial cell disorders, vaginal discharge, and ectoparasites ( Table 264-1 ). Gender inclusive models ( Chapter 215 ) and programs of…

Approach to the Patient with Urinary Tract Infection

Definitions Urinary tract infection (UTI) is bacterial or fungal infection of urine with associated signs or symptoms. The clinical presentation varies from cystitis (bladder or lower tract infection) to pyelonephritis (renal or upper tract infection) and urosepsis (systemic inflammatory response syndrome or septic shock from a urinary source). Asymptomatic bacteriuria is best considered a state of colonization that requires treatment in only specific clinical circumstances. Urethritis…

Approach to the Patient with Suspected Enteric Infection

Definition Enteric infections are endemic in many low-income countries but may also be contracted from contaminated food or water in developed countries. Symptoms may range from minimal gastrointestinal distress to life-threatening watery diarrhea or dysentery. Epidemiology Worldwide, enteric infections are a leading cause of morbidity. In low- and middle-income countries without access to clean water and basic sanitation, young children are disproportionately affected with acute diarrheal…

Prevention and Control of Health Care–Associated Infections

The Burden of Health Care–Associated Infections Epidemiology The Centers for Disease Control and Prevention (CDC) defines health care–associated infections as infections that patients acquire during the course of receiving health care treatment for other conditions. Nosocomial infection is a term that refers specifically to a health care–associated infection that develops in association with hospital care. The development of infection during the course of health care is…

Approach to Fever and Suspected Infection in the Immunocompromised Host

Definition Healthy individuals possess robust antimicrobial defense systems that include physical barriers in the form of skin and mucosal membranes, innate immune defenses that are conserved through evolution, and adaptive (“acquired”) immune defense systems ( Chapter 35 ). These systems, which are highly interconnected, work in concert through an array of defensive surfaces, cells, and soluble factors to protect a host from potential microbial assailants. The…

Approach to Fever or Suspected Infection in the Normal Host

Overview of Fever Definition The traditional definition of a normal temperature as 98.6° F (37.0° C) came from a study more than 150 years ago, when 98.6° F (37.0° C) was the mean temperature from over 1 million axillary temperature measurements in 25,000 patients. Multiple more recent studies show contemporary axillary temperatures to be lower, with a mean axillary temperature of 96.75° F (36° C) and…

Principles of Anti-Infective Therapy

Selecting Antimicrobial Therapy Empirical Antimicrobial Therapy It is rare that antimicrobial therapy is instituted for a serious infection with full knowledge of the identity and antibiotic susceptibilities of the specific pathogen, so empirical antibiotic therapy typically must be initiated based on presumptions regarding the nature of the infection. The first challenge is to assess whether the patient likely has an infection and, if so, where is…

The Human Microbiome

The human microbiome has received considerable attention as a previously underappreciated factor in human health and disease. Alterations in the microbiome are associated with several clinical conditions, and restoration of a normal intestinal microbiome can be beneficial in selected situations. Definitions The so-called normal flora of microbes that live in and on the human body are part of the normal human microbiome. Although most attention has…

Introduction to Microbial Disease: Pathophysiology and Diagnostics

Infectious diseases have profoundly influenced the human genome and the course of human history. As of early 2023, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; Chapters 335 to 337 ) infection has caused nearly 7 million deaths worldwide. Beginning in the 1980s, acquired immunodeficiency syndrome (AIDS; Chapters 353 to 359 ) disrupted the social fabric of many countries, especially in Africa, and distressed health care systems…

Surgical Treatment of Joint Diseases

Epidemiology Estimates of the prevalence of arthritis and other rheumatic diseases demonstrate the enormous impact that these conditions have on the U.S. populace and the health care system in general. Over 21% of U.S. adults report physician-diagnosed arthritis. Osteoarthritis ( Chapter 241 ), which is the most prevalent form, affects upward to 31 million U.S. adults. Arthritis is already the leading cause of disability in the…