Infectious diseases comprise those illnesses that are caused by microorganisms or their products. Clinical manifestations of infection occur only when sufficient tissue injury has been inflicted directly by microbial products (e.g., endotoxins and exotoxins), or indirectly by host responses (e.g., cytokines and hydrolytic enzymes released by polymorphonuclear leukocytes). Despite the extraordinary recent advances that have occurred in therapeutics for infectious diseases, a number of basic principles should be followed to prescribe antimicrobials and vaccines is an optimal manner.
Epidemiologic and virulence factors in infectious diseases
Before appropriate therapy can be given for an infectious disease, consideration of epidemiologic factors is essential. This section does not fully discuss the epidemiology (the determinants, occurrence, distribution, and control of health and disease) of infectious diseases. However, a number of basic principles and historical points are worth emphasizing.
Documentation of infection
Symptoms and physical signs are frequently supportive of a diagnosis of infection but rarely are pathognomonic. For example, the activation of the acute inflammatory response is the most common way in which the clinical manifestations of infection become apparent. However, noninfectious conditions may also activate the same inflammatory mechanisms; therefore, the symptoms and signs of inflammation are by no means specific for infection.
Antimicrobial therapy: general principles
A wide variety of antimicrobial agents is available to treat established infections caused by bacteria, fungi, viruses, or parasites. This section will cover the general principles of antimicrobial therapy and will also include illustrative clinical problems to emphasize proper decision-making in using antimicrobials.
Toxicity of Antimicrobial Therapy
The mechanisms associated with common adverse reactions to antimicrobials include dose-related toxicity that occurs in a certain fraction of patients when a critical plasma concentration or total dose is exceeded, and toxicity that is unpredictable and mediated through allergic or idiosyncratic mechanisms. For example, certain classes of drugs such as the aminoglycosides are associated with dose-related toxicity.
Management of selected clinical conditions
This section is devoted to topics that exemplify important considerations in treatment and prophylaxis with antibiotics. Overviews are provided by discussing selected clinical settings and the therapeutic issues they raise.
Nucleoside analogs
Nucleoside analog reverse transcriptase inhibitors have formed the backbone of anti-human immunodeficiency virus therapy for the last decade (see Table Characteristics of Nucleoside Reverse Transcriptase Inhibitors). Reverse transcription is necessary for human immunodeficiency virus RNA to be used as a template to produce viral DNA, which can be integrated into the cellular genome.
Management of the Febrile Neutropenic Patient
Consideration of treatment of the febrile neutropenic patient includes a brief summary of risk factors, organisms responsible for the disease, workup and management of a patient with respect to antimicrobial therapy, and immunoenhancement. Many clinical disease entities can cause a spectrum of immune suppression, and solid and hematologic tumors vary with respect to the degree of immune suppression they produce. Neutropenia is defined as an absolute neutrophil count that is less than 1000 cells/mm3. As the count falls below 1000 cells/mm3, the risk of infection increases.
Management of Bacterial Meningitis
Meningitis used to be a disease that occurred primarily in children younger than 12 years. The advent of a vaccine for Haemophilus influenzae has led to a marked change in the epidemiology of meningitis in developed countries.
Management of Infective Endocarditis
Infective endocarditis is a microbial infection of the endothelial lining of the heart. The characteristic lesion is a vegetation (a mass comprised of fibrin, platelets, microorganisms and their product or products on a valve leaflet). Multiple valves may be involved, as may any part of the endothelium of the heart.