Development of quality control procedures for the human immunodeficiency virus type 1 antibody enzyme-linked immunosorbent assay.

A standardized pool of human sera that was positive for human immunodeficiency virus type 1 (HIV-1) antibody was developed. This positive control serum was used to analyze test differences among eight laboratories, among the HIV-1 antibody test kits of three different manufacturers, among different lots of the same test kit, and among pipetting devices and techniques. The standardized pool of human sera was tested 327 times by the different laboratories. In terms of positive tests, a reproducibility of 99.69% was achieved; however, significant test variance among laboratories, among test kit lots, and among pipetting devices and techniques could be demonstrated if the tests were compared on the basis of the net positive optical density (OD) value. This value was calculated by subtracting the cutoff OD value (i.e., the value below which an OD value was considered negative for HIV-1 antibody) from the observed OD value of the standardized pool of human sera. The results obtained suggest that this strategy can be used for proficiency testing, for monitoring the quality of HIV-1 antibody enzyme-linked immunosorbent assay reagents, and for evaluating pipetting devices and techniques.

Comparison of sedimentation and flotation techniques for identification of Cryptosporidium sp. oocysts in a large outbreak of human diarrhea.

Cryptosporidiosis, previously seen mostly among immunocompromised patients, is now recognized among immunocompetent patients. During a large outbreak of cryptosporidiosis in two day-care centers, we compared two procedures for the demonstration of the organism in preserved stool specimens. Of 703 stool specimens tested by both techniques, Sheather sucrose flotation (SSF) identified 127 (18.1%) as positive for Cryptosporidium sp. oocysts. Ritchie Formalin-ethyl acetate sedimentation (F/EA) plus a modified cold Kinyoun acid-fast stain (MCK) of the sediment identified 129 (18.4%) as positive for Cryptosporidium sp. oocysts. The degree of agreement between the two tests was statistically highly significant (P less than 0.0001). A total of 161 (22.9%) were positive by one technique or the other; 95 (13.5%) were positive by both techniques. A total of 32 specimens were positive by SSF but negative by F/EA plus MCK, and 34 specimens were positive by F/EA plus MCK but negative by SSF. The discrepancies between the two techniques occurred in stool specimens that contained rare to a few oocysts. Other parasitic forms were found by both techniques. F/EA plus trichrome staining recovered 126 (17.9%) specimens with Giardia lamblia, whereas SSF recovered only 42 (6.0%) specimens with G. lamblia. No association (chi 2 = 0.02, P = 0.89) was observed between the presence of G. lamblia and Cryptosporidium sp. in these stool specimens. We concluded that F/EA plus MCK of the sediment was as effective in the concentration and identification of Cryptosporidium sp. oocysts as SSF. F/EA plus MCK may be advantageous as a single concentration method for general parasitology when Cryptosporidium sp. is also being sought.

Epidemiologic and clinical characteristics of persons with serologic evidence of E. canis infection.

The results of a serosurvey of Oklahomans for the presence of antibody to Ehrlichia canis is reported. Paired serum specimens, from patients lacking the serologic criteria for diagnosis of Rocky Mountain spotted fever (RMSF), were tested. A four-fold increase in E. canis-IFA antibody was found in 16/144 (11 percent) of these paired serum samples. Patients with serologic evidence of E. canis infection had a mean age of 34 years, 69 percent were male, and 63 percent lived in a town less than 10,000 population. Signs and symptoms included: fever 94 percent, headache 94 percent, fatigue 94 percent, anorexia 81 percent, nausea 60 percent, and rash 44 percent. When compared to control patients, whose sera were submitted for RMSF testing but did not meet serologic criteria for RMSF or E. canis, case-patients were more likely to have had leukopenia (OR = 4.9, 95 percent Cl = 1.2, 19.0) and tick exposure (OR = 9.5, 95 percent Cl = 1.4, 62.7). The results suggest E. canis, or a closely related agent, is a cause of human illness. Ticks are probable vector.