Tags: Allergy

Dermatophytes

Essentials of Diagnosis Characteristic pattern of inflammation on glabrous skin surfaces. The active border of infection is scaly, red, and slightly elevated. Wet mount preparation with potassium hydroxide (10-20%). Skin scraping of the active border shows branching, translucent, rod-shaped filaments (hyphae) in keratinized material under low-power microscopy (10-40×). Hyphae are uniformly wide and regularly septated. Wood’s light examination (UV light at 365 nm) shows blue-green fluorescence for Microsporum canis and Microsporum audouinii. Trichophyton schoenleinii is pale green, and tinea versicolor shows white-yellow fluorescence. Culture should be performed with hair, nail, and skin specimens from particularly inflammatory lesions, to make a definitive mycologic diagnosis. General Considerations Dermatophytes are molds that infect keratinized …

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Histoplasma Capsulatum

Essentials of Diagnosis Thin-walled oval yeast measuring 2-4 mm in diameter. Dimorphic: mycelial in nature, yeast in tissue. Endemic within Ohio and Mississippi River Valleys. Associated with activities that disturb dust or soil enriched with bird, chicken, and bat excrement. Complement fixation antibody titer 1:32 or greater. Simultaneous appearance of anti-H and anti-M antibodies. Infection most often is asymptomatic or may cause chronic pulmonary infection; less commonly, disseminated infection involving the adrenals, ulcerative gastroenteritis lesions, or central nervous system. Recovery of organism from culture of tissue, blood, sputum, or other source. General Considerations A. Epidemiology. Histoplasma capsulatum, the etiologic agent of histoplasmosis, is an endemic, dimorphic fungus that causes a wide …

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Rocky Mountain Spotted Fever (RMSF)

Essentials of Diagnosis Key symptoms and signs: abrupt onset of high fevers, headaches, myalgias, malaise, and a flu-like illness 3-12 days after tick bite; rash (80-90% of patients, initially maculopapular, then petechial, classically involving the palms and soles). Predisposing factors: tick exposure (April through September), pet owners, animal handlers, and outdoor activities. Commonest geographic location of infection: rural. Confirmatory serology via IFA. PCR with blood or skin biopsy: sensitive and specific but not widely available. General Considerations RMSF is caused by Rickettsia rickettsii and is an acute tick-borne illness occurring during seasonal tick activity. The disease is characterized by acute onset of fever, headache, and a rash of the extremities spreading …

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Brucella, Francisella, Pasteurella, Yersinia, & Hacek

BRUCELLOSIS Essentials of Diagnosis • Suspected in patients with chronic fever of unknown etiology who have a history of occupational exposure or come from a high prevalence area. • Leukopenia. • Blood culture or bone marrow cultures on appropriate media. • Serum antibody titer = 1:160. • Polymerase chain reaction. General Considerations Brucellosis (also called undulant fever, Mediterranean fever, Malta fever) is an infection that causes abortion in domestic animals. It is caused by one of six species of Brucella coccobacilli. It may occasionally be transmitted to humans, in whom the disease could be acute or chronic with ongoing fever and constitutional symptoms without localized findings. A. Epidemiology. Brucellosis is transmitted …

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Infection in Patients With Aids

Paeruginosa infections may occur in patients with AIDS. Risk factors for infection include a CD4 count of < 100 cells/mL3, neutropenia or functional neutrophil defects, intravascular catheterization, hospitalization, and prior use of antibiotics including ciprofloxacin or trimethoprim-sulfamethoxazole. Many cases are community acquired. Bacteremia is common, and the lung or an intravenous catheter is the most frequent portal of entry. An impaired ability to mount immunotype-specific antibodies to Pseudomonas lipopolysaccharide antigen has been noted in HIV-positive individuals with bacteremia. Relapse is frequent, and mortality is high, 40%. Pneumonia is usually associated with cavitation and a high relapse rate. Bacterial sinusitis is an important and frequently undetected illness in HIV-positive individuals, and P …

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Enterococci

Essentials of Diagnosis • Gram stain shows gram-positive cocci that occur in singles, pairs, and short chains; recovery of microorganism from culture of blood or other sterile source. • Lancefield group D antigen. • Clinical isolates: Enterococcus faecalis, 74%; E faecium, 16%; other species, 10%. • Facultative anaerobes grow in 6.5% NaCl at pH 9.6 and at temperatures ranging from 10 °C to 45 °C, and grow in the presence of 40% bile salts and hydrolyze esculin and L-pyrrolidonyl-ß-naphthylamide. • Infections typically of a gastrointestinal or genitourinary origin. • The most common infections are urinary tract infection, bacteremia, endocarditis, intra-abdominal and pelvic infection, and wound and soft tissue infection. General Considerations …

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Streptococcus Pneumoniae

Essentials of Diagnosis • Most common infections include pneumonia, meningitis, sinusitis, and otitis media. • Predisposing factors include extremes of age (ie, infants and elderly) and underlying host defects in antibody, complement, and splenic function. • Transmission is human to human both in the community and nosocomially. • Pneumonia: productive cough, fever, chills, sweats, and dyspnea; lobar or segmental consolidation on chest x-ray; lancet-shaped gram-positive diplococci on Gram stain of sputum or growth of S pneumoniae from sputum, blood, or pleural fluid. • Meningitis: headache, stiff neck, fever, chill, and photophobia; nuchal rigidity, Kernig’s or Brudzinski’s sign; lancet-shaped gram-positive diplococci on Gram stain of cerebrospinal fluid (CSF), growth of S pneumoniae …

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Staphylococci

STAPHYLOCOCCUS AUREUS Essentials of Diagnosis • Large gram-positive cocci (0.7-1.5 um in size). • Colonies surrounded by zone of hemolysis on blood agar. • Colonies pigmented pale yellow to deep orange macroscopically. • Cluster in grapelike bunches microscopically. • Biochemically differentiated from streptococci by presence of the enzyme catalase. • Biochemically differentiated from other staphylococci by presence of the enzyme coagulase. • Analysis of chromosomal DNA can identify clonal isolates (useful in epidemiologic studies). General Considerations A. Epidemiology. Staphylococcus aureus colonizes the human skin, vagina, nasopharynx, and gastrointestinal tract. Colonization occurs shortly after birth and may be either transient or persistent. Published studies differ widely in estimates of the prevalence of …

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Primary Bacteremia & Endocarditis

Staphylococci (both S aureus and CoNS) have emerged as the two most common organisms cultured from patients with primary bloodstream infections. The term “primary bacteremia” refers to positive blood cultures without an identifiable anatomic focus of infection. Differentiation of primary bacteremia from infective endocarditis (IE), in which infection of the cardiac valves leads to continuous bacterial seeding of the bloodstream, may challenge even the most experienced clinician. Primary S aureus bacteremia is associated with insulin-dependent diabetes, the presence of a vascular graft, and, most significantly, the presence of an indwelling intravascular catheter. Risk factors for IE include structurally abnormal valves, recent injection drug use, and the presence of a prosthetic cardiac …

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Rubella

General Considerations A. Epidemiology. The epidemiology of rubella, commonly referred to as German measles or 3-day measles, has changed dramatically in the past 30 years, owing exclusively to the widespread use of the rubella live attenuated virus vaccine. Before the use of this vaccination (1969), the virus had an epidemic cycle of 6-9 years. It is primarily a winter and early spring infection. The incidence of rubella infection in developed countries has declined by 99%, compared with pre-vaccine era data. In the vaccine era, current data suggest that 10% of young adults are still susceptible. The majority of these young adults lack vaccination. A major concern of rubella is infection of …

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