Biomedical subjects
Publications and source records attributed to C T Le.
The general procedure for sample size determination based upon the confidence interval approach is reviewed and presented for both absolute and relative precision stipulations. The relationship between precision and sample size is discussed and methods for sample size determination for clinical trials are presented and illustrated with numerical examples.
Asplenic persons are at increased risk of overwhelming sepsis caused by Streptococcus pneumoniae. Vaccination with polyvalent pneumococcal polysaccharide has been shown to stimulate a nearly normal antibody response in these individuals, indicating that active vaccination might prevent pneumococcal disease in this population. To obtain information on the duration of protective levels of pneumococcal antibody, 33 asplenic children were vaccinated and antibody levels were measured at intervals for up to 4 1/2 years after vaccination. Significant antibody decline was observed in children who had undergone splenectomy because of trauma, but antibody decline was not observed in children whose spleens had been removed because of hereditary spherocytosis. There was a highly significant difference in rates of antibody decline among the 12 antibody serotypes measured: types 1, 4, 6A, 7F, 8, 19F, and 23F showed the greatest decline. Based on measured rates of antibody decline, subprotective antibody levels (antibody nitrogen less than 300 ng/ml) for types 7F, 8, and 19F would be reached 1 to 2 years after vaccination; type 6A never reached the protective level; and antibodies against the remaining eight types either were within the protective range initially or did not show significant decline. Asplenic children may benefit from revaccination with certain antigen types (7F, 8, and 19F) 1 to 2 years after initial vaccination.
In 1981, 54 Epstein-Barr virus-seronegative pregnant women in the Sacramento-Davis area of California were observed prospectively for an average duration of 12.1 months for Epstein-Barr virus-seroconversion. Only one seroconverted. Two of the 54 women remained negative for Epstein-Barr virus antibody 4.5-5.0 months after their husbands were proved to be Epstein-Barr virus excreters. Short of experimental pharyngeal introduction of the virus into human volunteers, these data provide the most direct evidence possible that the intimate exposure of Epstein-Barr virus-seronegative adults to the virus does not necessarily result in infection.
Audiometric and tympanometric findings were compared among 129 patients with clinically manifest persistent otitis media (OM) with effusion. Ears with thick effusion (mucoid OM) had significantly larger air-bone gaps and higher prevalence of flat tympanograms than either of the thin effusion types (purulent [POM] or serous OM [SOM]) or ears with no effusion (dry). Ears with thin effusion (POM and SOM) had similar air-bone gaps, thresholds for air and bone conduction, and prevalences of flat and underpressure tympanograms. Ears with no effusion had significantly smaller air-bone gaps, slightly poorer bone conduction thresholds, and lower prevalence of flat tympanograms than ears with effusion (MOM, POM and SOM). Ears with clinically manifest OM and no effusion at tympanocentesis appear to represent patients with a spontaneously resolved episode of OM with thin effusion (POM or SOM) or with ears that evacuated during anesthesia prior to tympanostomy.
Susceptibility to Epstein-Barr virus (EBV) infection in 1,729 pregnant women was evaluated by screening for EBV antibodies. Fifty-eight subjects (3.4%) had no detectable EBV antibody and were presumably susceptible. Of the 54 women who agreed to participate in this study, none acquired EBV antibody during pregnancy. Our results are in general agreement with some published reports that primary EBV infection during pregnancy is rare. The role of EBV in congenital infections and perinatal morbidity remains to be defined.
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Non-invasive methods for distinguishing different types of otitis media would have clinical value in predicting otologic morbidity. Two such methods, otoscopy and tympanometry, were used in two experimental models of otitis media to determine whether there are unique otoscopic and tympanometric characteristics of serous and purulent otitis media. A flat (type B or B+) tympanogram and yellow tympanic membrane each had a high likelihood of predicting middle ear effusion in these models, and the best prediction was obtained using both parameters simultaneously. A yellow tympanic membrane color predicted purulent otitis media in one model but did not distinguish purulent from serous ears in the other model. In one model, serous otitis media was frequently associated with a type C (negative pressure) tympanogram. Tympanometry provided a valuable adjunct to otoscopy in detecting effusion and in distinguishing serous and purulent disease. These observations may apply to otitis media in humans, although the variable etiologies of otitis media in humans may confound the ability of otoscopy and tympanometry to distinguish middle ear effusion types.
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The recently accepted international classification for otitis media was applied to a study population of 898 children less than 12 years of age having otitis media with effusion persisting at least three months. Mucoid effusion was aspirated from 48% of ears, was found more often in younger than older patients, was more often bilateral, and was a more stable state during longitudinal observation than was serous otitis media or purulent otitis media (POM). Serous otitis media occurred in only 10% of ears, but was found more often than in younger patients; POM was found in only 7% of ears. Otoscopy did not distinguish among the three effusion types. Known middle-ear pathogens were cultured more often behind red and bulging tympanic membranes from these cases of chronic effusion than behind membranes lacking these characteristics. These observations provide an epidemiologic and clinical base for further investigations of these otitis media types.
Mean survival of 110.5 months (9 yr. 2.5 months) for spinal cord-injured persons who died between 1963 to 1976 compared favorable with the figure of 52.8 months (4 yr, 4.8 months) calculated in 1955 by Dietrick and Russi [1]. If suicides were not considered, then mean longevity for the deceased patients would be 126 months (10 yr, 6 months). The leading causes of death were related to the cardiovascular system, respiratory system, suicide and the urinary tract.
Polyvalent pneumococcal vaccine was administered to 7 patients with chronic renal failure, 14 patients on chronic hemodialysis, 14 splenectomized and 11 nonsplenectomized renal allograft recipients, and 14 normal adults. Ninety-three percent of normal subjects had at least a twofold rise in serum antibody concentration after vaccination, with a geometric mean antibody concentration after vaccination greater than 200 ng N/ml. The response to vaccination in hemodialysis patients was similar to that in normal persons. Renal failure patients showed impaired antibody synthesis in response to the vaccine, with 43% achieving at least a twofold rise in antibody concentration. Allograft recipients had a lower antibody concentration before as well as after vaccination, and among splenectomized recipients the prevaccination antibody concentration was directly related to the interval between transplantation and antibody determination. But, 80% of allograft recipients achieved a twofold rise in antibody concentration after vaccination. The response to pneumococcal vaccine was quantitatively similar for splenectomized and nonsplenectomized allograft recipients.
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Three cases of tick-borne fever diagnosed during the summer of 1979 are reported and the ecoepidemiology, clinical manifestations, and treatment of this infection are reviewed. Although challenging, the diagnosis can be made easily if specific historical clues are sought and the patient's blood smear is carefully examined. The diagnosis of this condition early in its course can save clinicians and patients the anxiety and cost of the work-up of a "fever of unknown origin." Since vacationing in the national parks and forests has become increasingly popular among many American families, tick-borne relapsing fever should be considered in any patient with an acute or recurrent fever of unknown origin who exhibits nonspecific symptoms of an undifferentiated "viral illness," and who gives a history of sleeping overnight in log cabins in the coniferous forests of the Western mountains of the United States.
Three structurally and antigenically similar capsular polysaccharides, two derived from group C Neisseria meningitidis (O-acetyl-positive and O-acetyl-negative variants) and one from Escherichia coli K92, which cross-reacts with polysaccharide from group C N. meningitidis, were compared for their ability to induce anticapsular and bactericidal antibodies to group C N. meningitidis in adult volunteers. All three vaccines elicited group C-specific serum antibodies. The vaccine derived from the O-acetyl-negative variant was the most immunogenic of the three vaccines. With use of radiolabeled O-acetyl-positive group C N. meningitidis polysaccharide antigen, the geometric mean titers of antibody in serum were 41.7 microgram/ml to the O-acetyl-negative variant, 22.8 microgram/ml to the O-acetyl-positive variant, and 7.1 microgram/ml to E. coli K92. Antibodies induced by all three vaccines were bactericidal for both of the group C N. meningitidis polysaccharide variants. An inverse relation between the comparative immunogenicity of the O-acetyl-negative polysaccharide and the virulence of group C N. meningitidis was found.