Primary host defenses
Anatomic barriers
Intact skin surfaces
Nose hairs
Respiratory tract cilia
Coughing and flow of respiratory tract fluids and mucus
Swallowing and gastrointestinal (GI) tract peristalsis
Physiologic barriers
High or low pH and oxygen tension (prevents proliferation of organisms)
Chemical inhibitors to bacterial growth (e.g., proteases)
Bile acids
Active lysozymes in saliva and tears
Fatty acids on skin surfaces
Secondary host defenses (physiologic barriers)
Responses of complement, lysozymes, opsonins, and secretions
Phagocytosis
Immunoglobulin A (IgA), IgG, and IgM antibody formation
Cell-mediated immune responses
TABLE 7.1 Some Common Pathogens Detectable in Body Tissues and Fluids by Diagnostic Methods
Nasopharynx and Oropharynx
Sputum
Feces
β-Hemolytic streptococci
Bordetella pertussis
Mycoplasma spp.
Moraxella catarrhalis
Herpes simplex virus
Pseudomonas spp.
Candida albicans
Corynebacterium diphtheriae
Haemophilus influenzae
Neisseria meningitidis
Streptococcus pneumoniae
Staphylococcus aureus
Enterobacteriaceae
Cryptococcus neoformans
Respiratory syncytial virus
Influenza viruses
Parainfluenza viruses
Adenovirus
Rhinovirus
Coronavirus
Blastomyces dermatitidis
Bordetella pertussis
Candida albicans
Coccidioides immitis
Influenza viruses
Streptococcus pneumoniae
Pseudomonas spp.
Haemophilus influenzae
β-Hemolytic streptococci
Histoplasma capsulatum Klebsiella spp.
Mycobacterium spp.
Yersinia pestis
Francisella tularensis
Staphylococcus aureus
Mycoplasma spp.
Legionella spp.
Chlamydophila pneumoniae
Pneumocystis
Campylobacter jejuni
Clostridium botulinum
Entamoeba histolytica
Escherichia coli Salmonella spp.
Shigella spp.
Staphylococcus aureus
Vibrio cholerae
Vibrio comma
Vibrio parahaemolyticus
Yersinia enterocolitica
Clostridium difficile
Rotavirus
Hepatitis A, B, and C
Giardia lamblia Cryptosporidium spp.
Norovirus
Aeromonas sp.
Plesiomonas sp.
Leptospira
Urine
Streptococcus agalactiae
Escherichia coli, other
Enterobacteriaceae
Enterococcus spp.
Neisseria gonorrhoeae
Mycobacterium tuberculosis
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus saprophyticus
Salmonella and Shigella spp.
Trichomonas vaginalis
Candida albicans and other yeasts
Staphylococcus epidermidis
Skin
Ear
Bacteroides spp.
Clostridium spp.
Fungi
Pseudomonas spp.
Staphylococcus aureus
Streptococcus pyogenes
Varicella zoster virus
Sarcoptes scabiei
Herpes simplex virus
Bacillus anthracis
Treponema pallidum
Aspergillus fumigatus
Candida albicans and other yeast
Enterobacteriaceae β-Hemolytic streptococci
Streptococcus pneumoniae
Pseudomonas aeruginosa
Staphylococcus aureus
Moraxella catarrhalis
Mycoplasma pneumoniae
Peptostreptococcus spp.
Bacteroides fragilis
Fusobacterium nucleatum
Influenza virus
Respiratory syncytial virus (RSV)
Cerebrospinal Fluid
Vaginal Discharge
Urethral Discharge
Bacteroides spp.
Cryptococcus neoformans
Haemophilus influenzae
Mycobacterium tuberculosis
Neisseria meningitidis
Streptococcus pneumoniae
Enteroviruses
Listeria monocytogenes
Streptococcus agalactiae
(Group B)
Staphylococcus spp.
Escherichia coli
Herpes simplex virus
Mycoplasma
β-Hemolytic streptococci
Candida albicans
Gardnerella vaginalis
Listeria monocytogenes
Mycoplasma spp.
Human papilloma virus
Neisseria gonorrhoeae
Treponema pallidum
Herpes simplex virus
Trichomonas vaginalis
Chlamydia trachomatis
Chlamydia trachomatis
Coliform bacilli
Herpes simplex virus
Neisseria gonorrhoeae
Treponema pallidum
Trichomonas vaginalis
Mycoplasma spp.
Ureaplasma urealyticum
Human papillomavirus
Mobiluncus spp. and
other anaerobes
Factors decreasing host resistance
Age: The very young and the very old are more susceptible.
Presence of chronic disease (e.g., cancer, cardiovascular disease, diabetes)
Use or history of certain therapeutic modalities, such as radiation, chemotherapy, corticosteroids, antibiotics, or immunosuppressants
Toxins, including alcohol, street drugs, legitimate therapeutic drugs, venom or toxic secretions from a reptile or insect, or other nonhuman bites or punctures
Others, including excessive physical or emotional stress states, nutritional state, and presence of foreign material at the site
Observe standard precautions. Clean the skin starting centrally and going out in larger circles. Repeat several times, using a clean swab or wipe each time. If 70% alcohol is used, it should be applied for 2 minutes. Tincture of iodine requires only 1 minute of cleansing.
Bypass areas of normal flora; culture only for a specific pathogen.
Collect fluids, tissues, skin scrapings, and urine in sterile containers with tight-fitting lids. Polyester-tipped swabs in a collection system containing an ampule of Stuart’s transport medium ensure adequacy of the specimen for 72 hours at room temperature.
Place the specimen in a biohazard bag.
Label specimens properly with the following information (institutional requirements may vary):
Patient’s name, age, sex, address, hospital identification number, and physician’s full name
Specimen source (e.g., throat, conjunctiva)
Time of collection
Specific studies ordered
Clinical diagnosis; suspected microorganisms
Patient’s history
Patient’s immune state
Previous and current infections
Previous or current antibiotic therapy
Isolation status—state type of isolation (e.g., contact, respiratory, wound)
Other requested information pertinent to testing
2. Avoid contaminating the specimen; maintain aseptic or sterile technique as required:
Special supplies may be required:
For anaerobes, sterile syringe aspiration of pus or other body fluid
Anaerobic transport containers for tissue specimens
Sterile specimen containers
Precautions to take during specimen collection include:
Care to maintain cleanliness outside container surfaces
Use of appropriately fitting covers or plugs for specimen tubes and bottles
Replacement of sterile plugs and caps that have become contaminated
Observation of standard precautions
Ensure the preservation of specimens by delivering them promptly to the laboratory. Many specimens may be refrigerated (not frozen) for a few hours without any adverse effects. Note the following exceptions:
Urine culture samples must be refrigerated.
CSF specimens should be transported to the laboratory as soon as possible. If this is problematic, the culture should be incubated (meningococci do not withstand refrigeration). Both culture bottles must be maintained at room temperature prior to being placed in the analyzer.
Blood culture bottles must be maintained at room temperature.
Transport specimens quickly to the laboratory to prevent desiccation of the specimen and death of the microorganisms.
For anaerobic cultures, no more than 10 minutes should elapse between time of collection and culture. Anaerobic specimens should be placed into an anaerobic transport container.
Feces suspected of harboring Salmonella or Shigella organisms should be placed in a special transport medium, such as Cary-Blair, if culturing of the specimen will be delayed longer than 30 minutes.
Ensure that specimen quantity is adequate. With few exceptions, the quantity of the specimen should be as large as possible. When only a small quantity is available, swabs should be moistened with sterile saline just before collection, especially for nasopharyngeal cultures.
Handle specimen collection in the following way:
Submit entire fluid specimen collected. Do not submit fluids on swabs.
Whenever possible, specimens should be collected before antibiotic regimens are instituted; for example, complete all blood culture sampling before starting antibiotic therapy.
TABLE 7.2 Bacterial Diseases and Their Laboratory Diagnosis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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The terms sensitive and susceptible imply that an infection caused by the bacterial strain tested is likely to respond favorably in the presence of the indicated antimicrobial agent.
The terms intermediate, partially resistant, and moderately susceptible mean that the bacterial strain tested is not completely inhibited by therapeutic concentrations of a test drug.
Indeterminate means that the bacterium has an MIC that approaches achievable blood and tissue concentrations. It implies clinical efficacy in body sites where the antibiotic is physiologically concentrated. The intermediate category also includes a buffer zone, which should prevent major errors due to technical factors.
The term resistant implies that the organism is not inhibited by the antibiotic. This infection is not likely to respond to treatment.
Some antimicrobial agents act in a bactericidal manner, meaning that they kill the organism. Others act in a bacteriostatic manner, meaning that they inhibit growth of the organism but do not necessarily kill it.
Bactericidal agents
Aminoglycosides
Cephalosporins
Metronidazole
Penicillins
Quinolones
Rifampin
Vancomycin
Bacteriostatic agents
Chloramphenicol
Erythromycin
Sulfonamides
Tetracycline
Emergence of strains of penicillin-resistant Neisseria gonorrhoeae, carbapenem-resistant enterobacteriaceae (CRE) and extended spectrum beta lactamases (ESBLs), methicillin-resistant (or oxacillin-resistant) S. aureus, amikacin-resistant Pseudomonas spp. or other gram-negative rods, and vancomycin-resistant Enterococcus spp. presents challenges to the clinician in regard to treatment. Many hospitals screen for methicillin-resistant S. aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) spp. so as to isolate patients infected with these organisms.
Sputum and bronchial aspirates and lavages are the best samples for diagnosis of pulmonary infection. Purulent sputum (5 to 10 mL) from the first productive cough of the morning should be expectorated into a sterile container. If the specimen is not processed immediately, it should be refrigerated. Pooled specimens collected over several hours are not acceptable. For best results, three specimens should be collected over several days. A prerequisite of good specimen collection is the use of sterile, sturdy, leak-proof containers placed into biohazard bags.
TABLE 7.3 Mycobacterial Infections and Their Laboratory Diagnosis
Causative Organism
Source of Specimen
Diagnostic Test
Mycobacterium tuberculosis
Sputum, urine, CSF, tissue, bone marrow
Culture and smear; skin test; DNA probe; nucleic acid amplification assay
Mycobacterium avium-intracellulare
Sputum, stool, CSF, tissue, blood, semen, lymph nodes
Culture and smear; DNA probe
Mycobacterium kansasii
Skin, joint, lymph nodes, sputum, tissue
Culture and smear
Mycobacterium leprae
CSF, skin, bone marrow, lymph nodes
Histopathologic examination of lesion
Mycobacterium marinum
Joint lesion, skin
Culture and smear
Mycobacterium xenopi
Sputum
Culture and smear
Mycobacterium fortuitum
Surgical wound, bone, joint, tissue, sputum
Culture and smear
Mycobacterium chelonae
Surgical wound, sputum, tissue
Culture and smear
AFB smears and cultures are done to determine whether TB-like symptoms are due to M. tuberculosis infection or infection from another mycobacterium and to aid in determining whether the TB is intrapulmonary or extrapulmonary.
If the patient is unable to produce sputum, an early-morning gastric sample may be aspirated and cultured. This specimen must be hand-delivered to the laboratory to be processed or neutralized immediately.
Patients with suspected renal disease should provide early-morning urine specimens collected for 3 days in a row. Pooled 24-hour urine collections are not recommended. Unless processed immediately, the specimen should be refrigerated.
If TB meningitis is suspected, at least 10 mL (2 mL in children) of CSF should be obtained.
Sterile body fluids, tissue biopsy samples, and material aspirated from skin lesions are acceptable specimens for mycobacterial cultures. Tissue should be placed in a neutral transport medium to avoid desiccation. Swab specimens are not suitable for mycobacterial culture.
Feces are commonly the first specimens from which MAI complex can be isolated in a patient with disseminated disease. An acid-fast stain can be performed directly.
MAI complex organisms can also be isolated from the blood of immunosuppressed patients.
Obtain a 5-mL venous blood sample (dark-green topped [sodium heparin] tube) for the QFT-G.
See description in Tuberculin Skin Test section.
A positive QFT-G result indicates that TB infection is likely.
A negative QFT-G result indicates that TB infection is unlikely but cannot be excluded.
Diabetes, silicosis, and chronic renal failure may decrease responsiveness to both the TST and QFT-G tests.
Treatment with immunosuppressive drugs has been shown to decrease the response to the TST.
Some of the hematologic disorders, such as leukemia and lymphoma, may decrease response to the TST and QFT-G test.
Explain test purpose and blood-drawing procedure.
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Interpret test results and counsel appropriately.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.
Typhus-like fevers
Spotted fever
Scrub typhus
Q fever
Other rickettsial diseases
Fever
Skin rashes
Parasitism of blood vessels
Prostration
Stupor and coma
Headache
Ringing in the ears
Dizziness
TABLE 7.4 Rickettsial Diseases and Their Laboratory Diagnosis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Multiple specimens may be necessary to detect a parasitic infection.
Most parasites found in humans are identified in blood or feces but may also be evident in urine, sputum, tissue fluids, or biopsy tissues.
Fecal specimens should not be contaminated with water or urine. All specimens should be labeled with the patient’s name, clinician’s name, identification number (if applicable), and date and time collected. Various commercial collection systems are available to allow collection of specimens at home, in a nursing institution, or in a hospital setting. Clear instructions should be communicated and given in writing to the patient to ensure proper collection. See Chapter 4, Stool Studies, for more information.
TABLE 7.5 Parasitic Diseases and Their Laboratory Diagnosis
Disease
Causative Organism
Source of Specimen
Diagnostic Tests
Amebiasis
Entamoeba histolytica
Stool, liver
Stool smear, rectal biopsy, serologic test, antigen test
Ascariasis
Ascaris lumbricoides
Stool, sputum
Ova and parasite examination, antigen test, rectal biopsy, serologic test
Cestodiasis of intestine (tapeworm disease)
Taenia saginatus, Taenia solium, Diphyllobothrium, Hymenolepis nana, Hymenolepis diminuta
Stool
Ova and parasite examination, Scotch tape test for Enterobius vermicularis
Chagas’ disease
Trypanosoma cruzi
Blood, spinal fluid
Giemsa- or Wright-Giemsa-stained smear
Cryptosporidiosis
Cryptosporidium parvum
Stool, lung, gallbladder
Ova and parasite examination, antigen test, direct fluorescent antibody test
Cysticercosis
Taenia solium larvae
Muscle and brain
Muscle and brain cyst biopsy, serology
Echinococcosis
Echinococcus granulosus
Sputum and urine, liver, spleen
Ova and parasite examination, direct microscopic examination, serologic test, Casoni’s skin test; liver and bone biopsy
Enterobiasis (pinworm disease)
Enterobius vermicularis
Stool
Scotch tape test
Filariasis
Wuchereria bancrofti, Brugia malayi, Loa loa
Blood
Blood smear, lymph node biopsy, serologic test
Giardiasis
Giardia lamblia
Stool, duodenal aspirate or biopsy
Ova and parasite examination, antigen test, direct fluorescent antibody test, microscopic examination of Entero test
Hookworm
Ancylostoma duodenale, Necator americanus
Stool
Ova and parasite examination
Isosporiasis
Kala-azar
Isospora belli
Leishmania donovani
Stool
Liver, bone marrow, blood
Ova and parasite examination
Giemsa- or Wright-Giemsa-stained smear and culture, lymph node and spleen biopsy
Malaria
Plasmodium falciparum, Plasmodium malariae, Plasmodium vivax, Plasmodium ovale
Blood, bone marrow
Giemsa- or Wright-Giemsa-stained smear
Acanthamoebiasis
Acanthamoeba culbertsoni
CSF, corneal biopsy or scraping
Smear and tissue culture
Naegleriasis
Naegleria fowleri
CSF
Smear
Sarcocystis
Sarcocystis hominis or Sarcocystis suihominis
Stool
Ova and parasite examination
Blastocystis
Blastocystis hominis
Stool
Ova and parasite examination
Onchocerciasis
Onchocerca volvulus
Skin
Skin biopsy with histopathologic exam
Paragonimiasis
Paragonimus westermani
Sputum, stool
Ova and parasite examination, serologic test, skin test
Scabies
Sarcoptes scabiei
Skin
Skin smear, direct examination
Schistosomiasis of intestine and bladder
Schistosoma mansoni, Schistosoma japonicum, Schistosoma haematobium
Stool, urine
Ova and parasite examination, serologic test, skin test, rectal, bladder, and liver biopsy
Strongyloidiasis
Strongyloides stercoralis
Stool, duodenal aspirate
Ova and parasite examination, serologic test
Toxoplasmosis
Toxoplasma gondii
Blood, tissue, CSF
Serologic test, tissue smear, biopsy
Trichinosis
Trichinella spiralis
Muscle
Serologic test, skin test, muscle biopsy
Trichomoniasis
Trichomonas vaginalis
Vagina, bladder, urethra
Vaginal and urethral smear and culture, DNA probe
Trichuriasis
Trichuris trichiura
Stool
Ova and parasite examination
Trypanosomiasis
Trypanosoma rhodesiense, Trypanosoma gambiense
Blood, spinal fluid, lymph node
Blood, spinal fluid and lymph node smear, serologic test
Visceral larva migrans
Toxocara canis, Toxocara cati
Liver
Serologic test, skin test, liver biopsy
Trematodes
Fasciola hepatica, Clonorchis sinensis, Fasciolopsis buski
Stool
Ova and parasite examination
When sputum is collected for ova and parasites, it should be “deep sputum” from the lower respiratory tract. It should be collected early in the morning, before the patient eats or brushes the teeth, and immediately delivered to the laboratory. See Appendix B, Guidelines for Specimen Transport and Storage, for more information.
General considerations
Eosinophilia may be an indicator of parasitic infection.
Protozoa and helminths, particularly larvae, may be found in organs, tissues, and blood.
Specimen-related considerations
Hepatic puncture can reveal visceral leishmaniasis. Liver biopsy may yield toxocaral larvae and schistosomal worms and eggs. Hepatic abscess material from the peripheral area may reveal more organisms than the necrotic center.
Bone marrow may be positive for trypanosomiasis and malaria when blood samples produce negative results. Bone marrow specimens are obtained through puncture of the sternum, iliac crest, vertebral processes, trochanter, or tibia.
Puncture or biopsy samples from a lymph node may be examined for the presence of trypanosomiasis, leishmaniasis, toxoplasmosis, and filariasis.
Mucous membrane lesion or skin samples may be obtained through scraping, needle aspiration, or biopsy.
CSF may contain trypanosomes and Toxoplasma organisms.
Sputum may reveal Paragonimus westermani (lung fluke) eggs. Occasionally, the larvae and hookworm of S. stercoralis or Ascaris lumbricoides may be expectorated during pulmonary migration. In pulmonary echinococcosis (hydatid disease), hydatid cyst contents may be found in sputum.
Specimens taken from cutaneous ulcers should be aspirated below the ulcer bed rather than at the surface. A few drops of saline may be introduced by needle and syringe to aspirate intracellular leishmanial organisms.
Corneal scrapings or biopsy specimens can be examined histologically or cultured for the presence of Acanthamoeba. This organism is rare but can cause keratitis among contact lens wearers.
Films for blood parasites are usually prepared when the patient is admitted. Samples should be taken at 6- to 18-hour intervals for at least 3 successive days.
TABLE 7.6 Fungal Diseases and Their Laboratory Diagnosis | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Dermatophytoses include superficial and cutaneous mycoses, such as athlete’s foot, ringworm, and “jock itch.” Species of Microsporum, Epidermophyton, and Trichophyton are the causative organisms.
Subcutaneous mycoses involve the subcutaneous tissues and muscles.
Systemic mycoses involve the deep tissues and organs and are the most serious of the three groups.
Clean the suspected area with 70% alcohol to remove bacteria. Use sterile techniques and standard precautions.
Scrape the peripheral erythematous margin of putative “ringworm” lesions with a sterile scalpel or wooden spatula and place the scrapings in a covered sterile container.
Clip samples of infected scalp or beard hair and place in a covered sterile container.
Pluck hair stubs out with tweezers because the fungus is usually found at the base of the hair shaft. Use of a Wood’s light in a darkened room helps identify the infected hairs.
Samples from infected nails should be procured from beneath the nail plate to obtain softened material from the nail bed. If this is not possible, collect shavings from the deeper portions of the nail and place them in a covered sterile container.
A Wood’s light is used to determine presence of a fungus directly on hair. A Wood’s light is a lamp that uses ultraviolet rays of 3660A. In a darkened room, infected hairs fluoresce a bright yellowgreen under the Wood’s light.
Direct microscopic examination of tissue samples placed on a slide is performed to determine whether a fungus is actually present. The potassium hydroxide (KOH) test or Calcofluor white stain test is used to detect the presence of mycelial fragments, arthrospores, spherules, or budding yeast cells and involves mixing the specimen with the reagent on a glass slide. The slide is then microscopically examined for fungal elements.
A fluorescent brightener, Calcofluor white, fluoresces when exposed to ultraviolet light. This reagent stains the fungi, causing them to exhibit a fluorescence that can be detected microscopically. It can be used on tissue and has the same sensitivity as KOH. Moreover, it allows for easier and faster detection of fungal elements. Calcofluor white-stained specimens can also be examined under bright-field or phase-contrast microscopy.
Cultures are done to identify the specific type of fungus. Fungi are slow growing and are subject to overgrowth by contaminating and more rapidly growing organisms. Fungemia (fungus in the blood) is an opportunistic infection, and often, a blood culture reveals the earliest suggestion of the causative organism.
For fungal serology tests, single titers greater than 1:32 usually indicate the presence of disease. A fourfold or greater rise in titer of samples drawn 3 weeks apart is significant. However, serologic diagnosis of Candida and Aspergillus species can be disappointing. Complement fixation tests for histoplasmosis and coccidioidomycosis can aid in the diagnosis of these diseases. The immunodiffusion test is helpful for the diagnosis of blastomycosis.
Antigen tests performed on urine specimens are available for the detection of disseminated Histoplasma capsulatum and Blastomyces dermatitidis. The urinary antigen test has a 92% sensitivity.
Skin
Nails
Hair
Ulcer scrapings
Pus
CSF
Urine
Blood
Bone marrow
Stool
Bronchial washings
Tissue biopsy specimens
Prostatic secretions
Sputum
TABLE 7.7 Spirochetal Diseases and Their Laboratory Diagnosis | ||||||||||||||||||||||||||||||||||||
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Borrelia appear in the blood at the onset of relapsing fever. Louse-borne relapsing fever is caused by Borrelia recurrentis, tick-borne relapsing fever by several other Borrelia species, and Lyme disease by Borrelia burgdorferi. To date, there is no evidence that Lyme disease is transmitted by person-to-person contact.
Treponema (Borrelia) vincentii is the species responsible for ulcerative gingivitis (trench mouth).
Treponema pallidum is the species responsible for venereal syphilis in humans.
Treponema pallidum subsp. pertenue is the causative agent of yaws (an infectious nonvenereal disease).
Treponema carateum causes pinta (carate).
Treponema pallidum subsp. endemicum is the cause of endemic nonvenereal syphilis (bejel).
Leptospira is the genus of microorganism responsible for Weil’s disease (infectious jaundice), swamp fever, swineherd’s disease, and canicola fever.
The organism is widely distributed in the infected person and appears in the blood early in the disease process.
After 10 to 14 days, the organisms appear in considerable numbers in the urine.
Patients with Weil’s disease show striking antibody responses; serologic testing is useful for diagnosis of this disease.
Streptobacillus moniliformis and Spirillum minor are the species responsible for rat-bite fever. Although this condition occurs worldwide and is common in Japan and Asia, it is uncommon in North and South America and most European countries. Cases in the United States have been linked to bites or scratches by infected rodents (such as rats, mice, and gerbils). The case fatality rate is 7-10% among untreated patients.
Obtain a 2-mL blood specimen in a red-topped tube.
For Lyme disease, a two-step process is used. The first step uses either ELISA or IFA. A second step, using a Western blot test, is performed to confirm a positive ELISA or IFA result. If the Western blot is negative, it suggests that step 1 was a false positive. (Ten proteins are used in the serodiagnosis of Lyme disease.)
Explain purpose and procedure. Symptoms of Lyme disease include rash (erythema migrans), arthritis, facial paralysis, tingling or burning sensations in the extremities, and meningitis.
Follow Chapter 1 guidelines for safe, effective, informed pretest care.
Interpret test results; monitor and counsel patient appropriately. Recommended treatment of patients with Lyme disease includes antibiotics (e.g., amoxicillin, doxycycline, and cefuroxime axetil).
Follow Chapter 1 guidelines for safe, effective, informed posttest care.
caused by rickettsiae. One species, Mycoplasma pneumoniae, is recognized as the causative agent of primary atypical pneumonia and bronchitis. Other species are suspected as possible causal agents for urethritis, infertility, early-term spontaneous abortion, rheumatoid arthritis, myringitis, and erythema multiforme.
Infection or Syndrome | Suspected Viral Agents |
Infants and Children | |
Upper respiratory tract infection | Rhinovirus, coronavirus, parainfluenza, adenovirus, respiratory syncytial virus, influenza, human metapneumovirus |
Pharyngitis | Adenovirus, Coxsackie A, herpes simplex, Epstein-Barr, rhinovirus, parainfluenza, influenza |
Croup | Parainfluenza, respiratory syncytial, human metapneumovirus |
Bronchitis | Parainfluenza, respiratory syncytial, human metapneumovirus |
Bronchiolitis | Respiratory syncytial, parainfluenza, human metapneumovirus |
Pneumonia | Respiratory syncytial, adenovirus, influenza, parainfluenza |
Gastroenteritis | Rotavirus, adenoviruses 40-41, calicivirus, astrovirus, Norovirus |
Adults | |
Upper respiratory tract infection | Rhinovirus, coronavirus, adenovirus, influenza, parainfluenza |
Pneumonia | Coxsackie B |
Gastroenteritis | Norovirus |
All Persons | |
Parotitis | Mumps, parainfluenza |
Myocarditis/pericarditis | Coxsackie and echoviruses |
Keratitis/conjunctivitis | Herpes simplex, varicella-zoster, adenovirus |
Pleurodynia | Coxsackie B |
Herpangina | Coxsackie A |
Febrile illness with rash | Enteroviruses |
Infectious mononucleosis | Epstein-Barr, cytomegalovirus |
Meningitis | Enteroviruses, lymphocytic choriomeningitis, herpes simplex virus |
Encephalitis | Herpes simplex, togaviruses, bunyaviruses, flaviviruses, rabies, enteroviruses, measles, human immunodeficiency virus (HIV), JC virus |
Hepatitis | Hepatitis A, B, C, non-A, non-B; delta agent; E |
Hemorrhagic cystitis | Adenovirus, BK virus |
Cutaneous infection with rash | Herpes simplex, varicella-zoster, enteroviruses, Epstein-Barr, measles, rubella, parvovirus, human herpesvirus 6 |
Hemorrhagic fever | Ebola, Marburg, Lassa, hantavirus |
Acute respiratory failure | Hantavirus |
Isolation of the virus in tissue culture remains the gold standard for detection of many common viruses. Diagnostic modalities include the following:
Tissue culture
Direct detection in specimens
Identification through specific cytopathic effect
Use of immunofluorescence and immunoperoxidase, latex agglutination, or ELISA to identify
Visualization through an electron microscope
Direct nucleic acid hybridization probe and nucleic acid amplification assay
Serologic studies for antigen-antibody detection are valuable in regard to viral disease. Epstein-Barr virus (EBV) and human hepatitis viruses are routinely serodiagnosed. Classically, a fourfold rise in antibody titer is used to identify a particular infectious agent, provided that the pathogenesis of the agent agrees with the symptoms of the infected patient. An acute-phase serum is collected within the first several days after symptom onset. A convalescent-phase serum is collected 2 to 4 weeks later. A fourfold difference in antibody titer between the two sera is statistically significant. Alternatively, detection of specific immunoglobulin M (IgM) suggests acute infection. IgG antibody without IgM suggests infection sometime in the past.
Available cell cultures vary greatly in their sensitivity to different viruses. One cell type or species may be more sensitive than another for detecting the virus in low titers. For example, human embryonic kidney (HEK) or monkey kidney (1 MK) can be used for adenovirus, enterovirus, herpes simplex, measles, influenza, parainfluenza, and rubella; however, HEK cannot be used for cytomegalovirus (CMV) or influenza.
The critical first step in successful viral diagnosis is the timely and proper collection of specimens. The choice of which specimen to collect depends on typical signs and symptoms and the suspected virus. Improper specimen choice and collection is one of the biggest factors in diagnostic delays.
Collect specimens for viruses as early as possible during the course of the illness, preferably within the first 4 days after symptom onset. If specimen collection is delayed for 7 or more days after symptoms appear, diagnosis will be compromised. Virus titers are highest in the early part of the illness, when the host has not yet mounted a robust immune response. Little neutralizing antibody is present. Detection of a virus by culture, direct detection, or serology is greatly enhanced when the virus titers are high.
Sampling procedure
For localized infection:
Direct sampling of affected site (e.g., throat swab, skin scraping)
Indirect sampling. For example, if CSF is the target sample in a central nervous system infection, the indirect approach would involve obtaining throat or rectal swabs for culture.
Sampling from more than one site, for example, in disseminated infection or with nonspecific clinical findings
TABLE 7.8 Viral Infections and Their Laboratory Diagnosis
Infection Type and Virus Information
Throat
Stool/Rectal Swab
CSF
Urine
Vesicle Fluid/Swab
Conjunctival Swab/Scraping
Other
Blood Serology
Additional Information
Respiratory
Adenovirus
X
Nasopharyngeal swab
Yes
Enterovirus
X
No*
Herpes simplex virus (HSV)
X
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