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Discussion of Presentation by Merlyn R. Rodrigues, MD, PHD, Et Al
DISCUSSION OF PRESENTATION BY MERLYN R. RODRIGUES, MD, PHD, ET AL CHANDLER R. DAWSON, MD SAN FRANCISCO, CALIFORNIA UNTIL recent years the laboratory diagnosis of human viral infections has only rarely provided information soon enough to contribute to the therapeutic decisions regarding individual patients. Most viral diagnostic laboratories even now are either research units or deal mainly with public health problems, eg, the identification of strains of influenza virus present in a population so that epidemics may be predicted accurately and appropriate vaccines distributed. There are more and more hospital-based virus diagnostic laboratories, however, that have proved their usefulness in the management of pediatric and adult viral infections. Dr Rodrigues and associates have applied presently available technology to identifying the infectious agents causing eye disease early in the course of the infection, when such information will contribute substantially to the management of a patient's problem.
The authors have identified several syndromes in which rapid diagnosis could be of benefit to the patient, specifically (1) acute follicular conjunctivitis, (2) linear and branching corneal epithelial ulcers, and (3) ulcerative lid lesions. One
Submitted for publication Oct 22, 1978. From the Francis I. Proctor Foundation, Univer· sity of California, San Francisco. Presented at the 1978 Annual Meeting of the American Academy of Ophthalmology, Kansas City, Mo, Oct 22-26.
might add to this list (4) chronic epithelial defects of the cornea. The usual causative agents of acute follicular conjunctivitis and their respective syndromes in~lude (1) adenovirus (pharyngoconJunctival fever and epidemi<; keratoconjunctivitis); (2) Chlamydia sp (inclusion conjunctivitis caused by sexually transmitted C trachomatis or C psittaci infections); (3) herpes simplex virus (herpetic blepha~o conjunctivitis); (4) Ne~castl.e. ~Is ease virus (NDV con)uncbV1bs); and (5) picornavirus 70 and coxsackievirus A24 (acute hemorrhagic conjunctivitis). Of thes~ ey~ .i~ fections, adenovirus conJunctivitis is by far the most common. Chlamydia! conjunctivitis is relatively infrequent, and cases of herpesvirus conjunctivitis are fortunately rare. Specific therapy, however, is available for chlamydia! infections (systemic tetracycline or erythromycin) and prophylactic treatment with antivirals (idoxuridine, adenine arabinoside, or trifluorothymidine) is necessary in herpesvirus lid and conjuctival infections. Thus specific and timely microb~ologic diagnosis would be useful m the management of these problems. Most work on the diagnosis of adenovirus and HSV eye infections has been based on isolation of the agent in cell culture .s~stems ?ron demonstration of a nsmg antibody titer in adenovirus infections. Isolation procedures are expensive and
465
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CHANDLER R. DAWSON
slow (some adenovirus isolates may appear only after 30 to 60 days of serial culture). Serologic evidence of a specific adenovirus strain can only be shown by an increase in antibody level in serum specimens taken during the acute illness and then at three to four weeks after onset. Thus the immunofluorescent technique described by Dr Rodrigues can give rapid results. Herpesvirus and chlamydia! follicular conjunctivitis can also be diagnosed by immunofluorescent techniques. 1 •2 Although our laboratory employed immunofluorescent staining for chlamydia! infections for ten years, the method was never widely used since the test demanded special reagents and considerable skill in interpretation by the microscopist. To detect chlamydia! infections of the eye, Giemsastained conjunctival smears and isolation in cell culture systems are now used; this technique is becoming more widely available in state and hospital laboratories. Chronic or indolent corneal ulcers are another condition in which rapid diagnosis of viral infection would be useful. 3 Frequently these cases have a previous history of herpes keratitis. The therapeutic decision facing the clinician is whether or not to employ antivirals. A test to indicate the presence of live HSV or viral antigens would help the physician decide on the need to continue or initiate antiviral therapy. Here again immunofluorescent staining techniques might be useful. A technique that may supplement most immunofluorescent tech-
OPHTH AAO
niques for diagnosis of acute viral infections is the enzyme linked immunosorbent assay (ELISA) method. With this highly sensitive procedure, it should be possible to detect either antigen (ie, the viral agent) or antibody to a particular virus. 4 Since the readout on this test is a simple color change in the prepared test tube or plate and reagents can be standardized and prepared in advance, the ELISA technique may well be developed commercially for common infections including adenoviruses, herpesvirus, and Chlamydia. Thus it is possible that most hospital and diagnostic laboratories will have some means for rapid diagnosis of these eye infections in the near future. In evaluating any new diagnostic procedure, the clinician must be aware of the sensitivity and specificity of the procedure. These two terms have precise technical meanings.5 Sensitivity is the ability of a test to identify as positive those persons who have a disease. It is the number of diseased persons with a positive test divided by the total number of persons tested with disease. Specificity is the ability of a test to classify as negative those persons without the disease. It is the number of nondiseased persons with a negative test divided by the total number of persons tested without disease. As an example, let us assume that (1) among 50 cases of acute follicular conjunctivitis, serologic tests reveal that 40 are caused by adenovirus and ten by other causes and (2) a new diagnostic test is positive in 35 of these adenovirus cases and in two of the nonadenovirus cases. The sensitivity of the test is it or 87%, and the specificity is ~ = 80%.
VOLUME 86 MARCH 1979
467
DISCUSSION
Usually highly sensitive tests (ie, one that detects most cases of a disease) have a low degree of specificity. Conversely, tests with a high specificity (ie, few false positive results) have a low to medium degree of sensitivity. Estimates of specificity and sensitivity would be necessary to estimate the benefits to be expected from a certain test. Such considerations are of paramount importance in screening for a single disease. Finally the cost of the test must be considered as well, since the cost of a viral isolation procedure or serology may well exceed that of an initial office visit to an ophthalmologist. The clinician must judge the value of each diagnostic procedure in relation to the patient's condition. The most important considerations are whether the results will be available soon enough and whether the results will assist in managing the patient's problem. From this point of view, the iden-
tification of herpes simplex virus or chlamydia! agent would clearly influence management of these chronic, recurrent infections that respond to chemotherapy. REFERENCES 1. Taber LH, Brasier F, Couch RB, et a!: Diagnosis of herpes simplex virus infection by immunofluorescence. J Clin Microbial 3:309-312, 1978.
2. Schachter J, Dawson CR: Laboratory diagnosis, in Human Chlamydia[ Infections. Littleton, Mass, PSG Publishing, Inc, 1978, p 273. 3. Font RL: Chronic ulcerative keratitis caused by herpes simplex virus: Electron microscopic confirmation in paraffin-em· bedded tissue. Arch Ophthalmol 90:382385, 1973. 4. Bidwell DE, Bartlett A, Voller A: Enzyme immunoassays for viral diseases. J Infect Dis 136 (October suppl) :274-278, 1977. 5. Wilson JMG, Jangner G: Principles and Practice of Screening for Disease. Geneva, Public Health Papers 34, World Health Organization, 1968.
The authors have identified several syndromes in which rapid diagnosis could be of benefit to the patient, specifically (1) acute follicular conjunctivitis, (2) linear and branching corneal epithelial ulcers, and (3) ulcerative lid lesions. One
Submitted for publication Oct 22, 1978. From the Francis I. Proctor Foundation, Univer· sity of California, San Francisco. Presented at the 1978 Annual Meeting of the American Academy of Ophthalmology, Kansas City, Mo, Oct 22-26.
might add to this list (4) chronic epithelial defects of the cornea. The usual causative agents of acute follicular conjunctivitis and their respective syndromes in~lude (1) adenovirus (pharyngoconJunctival fever and epidemi<; keratoconjunctivitis); (2) Chlamydia sp (inclusion conjunctivitis caused by sexually transmitted C trachomatis or C psittaci infections); (3) herpes simplex virus (herpetic blepha~o conjunctivitis); (4) Ne~castl.e. ~Is ease virus (NDV con)uncbV1bs); and (5) picornavirus 70 and coxsackievirus A24 (acute hemorrhagic conjunctivitis). Of thes~ ey~ .i~ fections, adenovirus conJunctivitis is by far the most common. Chlamydia! conjunctivitis is relatively infrequent, and cases of herpesvirus conjunctivitis are fortunately rare. Specific therapy, however, is available for chlamydia! infections (systemic tetracycline or erythromycin) and prophylactic treatment with antivirals (idoxuridine, adenine arabinoside, or trifluorothymidine) is necessary in herpesvirus lid and conjuctival infections. Thus specific and timely microb~ologic diagnosis would be useful m the management of these problems. Most work on the diagnosis of adenovirus and HSV eye infections has been based on isolation of the agent in cell culture .s~stems ?ron demonstration of a nsmg antibody titer in adenovirus infections. Isolation procedures are expensive and
465
466
CHANDLER R. DAWSON
slow (some adenovirus isolates may appear only after 30 to 60 days of serial culture). Serologic evidence of a specific adenovirus strain can only be shown by an increase in antibody level in serum specimens taken during the acute illness and then at three to four weeks after onset. Thus the immunofluorescent technique described by Dr Rodrigues can give rapid results. Herpesvirus and chlamydia! follicular conjunctivitis can also be diagnosed by immunofluorescent techniques. 1 •2 Although our laboratory employed immunofluorescent staining for chlamydia! infections for ten years, the method was never widely used since the test demanded special reagents and considerable skill in interpretation by the microscopist. To detect chlamydia! infections of the eye, Giemsastained conjunctival smears and isolation in cell culture systems are now used; this technique is becoming more widely available in state and hospital laboratories. Chronic or indolent corneal ulcers are another condition in which rapid diagnosis of viral infection would be useful. 3 Frequently these cases have a previous history of herpes keratitis. The therapeutic decision facing the clinician is whether or not to employ antivirals. A test to indicate the presence of live HSV or viral antigens would help the physician decide on the need to continue or initiate antiviral therapy. Here again immunofluorescent staining techniques might be useful. A technique that may supplement most immunofluorescent tech-
OPHTH AAO
niques for diagnosis of acute viral infections is the enzyme linked immunosorbent assay (ELISA) method. With this highly sensitive procedure, it should be possible to detect either antigen (ie, the viral agent) or antibody to a particular virus. 4 Since the readout on this test is a simple color change in the prepared test tube or plate and reagents can be standardized and prepared in advance, the ELISA technique may well be developed commercially for common infections including adenoviruses, herpesvirus, and Chlamydia. Thus it is possible that most hospital and diagnostic laboratories will have some means for rapid diagnosis of these eye infections in the near future. In evaluating any new diagnostic procedure, the clinician must be aware of the sensitivity and specificity of the procedure. These two terms have precise technical meanings.5 Sensitivity is the ability of a test to identify as positive those persons who have a disease. It is the number of diseased persons with a positive test divided by the total number of persons tested with disease. Specificity is the ability of a test to classify as negative those persons without the disease. It is the number of nondiseased persons with a negative test divided by the total number of persons tested without disease. As an example, let us assume that (1) among 50 cases of acute follicular conjunctivitis, serologic tests reveal that 40 are caused by adenovirus and ten by other causes and (2) a new diagnostic test is positive in 35 of these adenovirus cases and in two of the nonadenovirus cases. The sensitivity of the test is it or 87%, and the specificity is ~ = 80%.
VOLUME 86 MARCH 1979
467
DISCUSSION
Usually highly sensitive tests (ie, one that detects most cases of a disease) have a low degree of specificity. Conversely, tests with a high specificity (ie, few false positive results) have a low to medium degree of sensitivity. Estimates of specificity and sensitivity would be necessary to estimate the benefits to be expected from a certain test. Such considerations are of paramount importance in screening for a single disease. Finally the cost of the test must be considered as well, since the cost of a viral isolation procedure or serology may well exceed that of an initial office visit to an ophthalmologist. The clinician must judge the value of each diagnostic procedure in relation to the patient's condition. The most important considerations are whether the results will be available soon enough and whether the results will assist in managing the patient's problem. From this point of view, the iden-
tification of herpes simplex virus or chlamydia! agent would clearly influence management of these chronic, recurrent infections that respond to chemotherapy. REFERENCES 1. Taber LH, Brasier F, Couch RB, et a!: Diagnosis of herpes simplex virus infection by immunofluorescence. J Clin Microbial 3:309-312, 1978.
2. Schachter J, Dawson CR: Laboratory diagnosis, in Human Chlamydia[ Infections. Littleton, Mass, PSG Publishing, Inc, 1978, p 273. 3. Font RL: Chronic ulcerative keratitis caused by herpes simplex virus: Electron microscopic confirmation in paraffin-em· bedded tissue. Arch Ophthalmol 90:382385, 1973. 4. Bidwell DE, Bartlett A, Voller A: Enzyme immunoassays for viral diseases. J Infect Dis 136 (October suppl) :274-278, 1977. 5. Wilson JMG, Jangner G: Principles and Practice of Screening for Disease. Geneva, Public Health Papers 34, World Health Organization, 1968.