Etiologic agents

Cefuroxime (35) is effective against community-acquired pneumonia in which ampicillin-resistant Haemophilus influence is the probable etiologic agent. Cefoxitin (23) is used to treat mixed aerobic—anaerobic infections including pelvic infections, intra-abdorninal infections, and nosocomial aspiration pneumonia. Cefonicid (31), because of its long half-life has been used in a once-a-day regimen to treat a variety of mild to moderate infections including community-acquired pneumonias, urinary tract infections, and infections of the skin and soft tissue (132,215). 

African sleeping sickness is a parasitic disease of increasing importance, with an estimated 300,000-500,000 cases annually. The etiological agents, T. brucei gambiense and T. brucei rhodesiense, are transmitted to humans by the bite of Tsetse flies. 

Malaria remains a major public health problem in many parts of the world, including Southeast Asia, sub-Saharan Africa and Latin America where an estimated 300-500 million people are infected. 1-3 million die of malaria every year. The etiologic agents of malaria are protozoan parasites of the genus Plasmodium. Of the four pathogens that can cause malaria in humans (Plasmodium falciparum, P. vivax, P. ovale,... 

Empiric antibiotic therapy is an appropriate approach to traveler s diarrhea. Eradication of the causal microbe depends on the etiologic agent and its antibiotic sensitivity. Most cases of traveler s diarrhea and other community-acquired infections result from enterotoxigenic (ETEC) or enteropathogenic (EPEC) Escherichia coli. Routine stool cultures do not identify these strains primary empiric antibiotic choices include fluoroquinolones such as ciprofloxacin or levofloxacin. Azithromycin may be a feasible option when fluoroquinolone resistance is encountered. 

Over 20 infectious agents have been incriminated as etiologic agents for many the causal relationship has been disproved, and for others there is conflicting evidence. Human herpesvirus 6 (HHV-6) is currently the most likely causative virus. HHV-6 may initiate the autoimmune processes of MS in one of two ways. First, HHV-6 is structurally similar to myelin basic protein. When T cells become sensitive to HHV-6, the cells may attack myelin basic protein. Second, HHV-6 may directly stimulate the complement cascade, activating autoimmune processes.5 Infection with HHV-6 alone cannot fully explain MS, because HHV-6 is found in 75% of all people, but MS is much more rare. 

Discuss testing that may need to be performed to suggest or confirm the etiologic agent (patch testing). 

Blood cultures are the essential laboratory test for the diagnosis and treatment of IE. Typically, patients with IE have a low-grade consistent bacteremia, with approximately 80% of cases having less than 100 CFU/mL in the bloodstream.1 Blood culture results are critical for determining the most appropriate therapy. Three blood culture sets should be drawn within the initial 24 hours to determine the etiologic agent. 

Ideally, to establish a causal relationship between caffeine and improved athletic performance, evidence would be obtained from epidemiological population studies, followed by careful, double-blind, placebo controlled experimental protocols isolating the purported etiological agent (caffeine), and eventually culminating with strong laboratory findings... 

Mycotic infections caused by dematiaceous fungi include chromoblastomycosis, mycetoma, phaeohyphomycosis, and sporotrichosis. In this chapter, only chromoblastomycosis, phaeohyphomycosis, and sporotrichosis will be considered. Sporotrichosis is treated here because the etiologic agent is dematiaceous in culture, even though the yeast form in tissue is hyaline. 

Rhinocladiella aquaspersa, previously known as Acrotheca aquaspersa, is a rare etiologic agent of chromoblastomycosis. Human cases of chromoblastomycosis caused by R. aquaspersa have occurred in Brazil and Mexico. 

S. schenckii, a dimorphic fungus, is considered the only pathogenic member of the genus Sporothrix. Recently, a new species, Sporothrix cyanescens, was added to the genus. Some of the isolates upon which the species description was based were isolated from patients with mycosis of human skin. Whether or not S. cyanescens is another etiologic agent of sporotrichosis remains to be proven. 

DNA viruses modulate the host immune response, e.g., most likely the etiologic agent of Kaposfs sarcoma, KSHV (human herpes vims —8), has captured complement-binding proteins, three cytokines (two macrophage inflammatory proteins and interleukin 6), bcl-2, interferon regulatory factors, interleukin 8 receptor. Certain retroviruses... 

Adachi J, Jiang ZD, Mathewson JJ, Verenkar MP, Thompson S, Martinez-Sandoval F, Steffen R, Ericsson CD, DuPont HL Enteroaggre-gative Escherichia coli as a major etiologic agent in traveler s diarrhea in 3 regions of the world. Clin Infect Dis 2001 32 1706-1709. 

Anaerobic bacteria are the most common etiologic agents in pneumonia that follows the gross aspiration of gastric or oropharyngeal contents. 

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