Multicentered study of viral acute lower respiratory infections in children from four cities of Argentina, 1993-1994.

This study describes the first multicentered study of acute lower respiratory infection viral etiology in young children from four different geographical areas of Argentina. A total of 1,278 children under 5 years of age, hospitalized in primary care centers from Buenos Aires, Córdoba, Santa Fé and Mar del Plata cities during a 2-year period were studied (1993-1994). Nasopharyngeal aspirates were investigated for respiratory syncytial virus (RSV), adenovirus, parainfluenza, and influenza A and B viruses by indirect immunofluorescence. Out of the patients studied, 946 (74%) were under 1 year of age. Viruses were detected in 399 patients (32%). RSV was observed in 25.3% of the samples, representing 78.2% of all viral positive cases. Adenoviruses were detected in 2.5% of the cases, parainfluenza in 2.2%, influenza A in 2.1%, and influenza B in 0.2%. Compared with other viruses, the higher RSV frequency was statistically significant (P < 0.000). Most RSV cases were detected between May and September with a significant peak in July (P < 0.000). Pneumonia was observed in 46% of the patients, bronchiolitis in 41% and other entities in 13%. The case fatality rate observed during the 2 year study was 0.73%. Most of the above respiratory viruses were detected in the four cities, however, the frequency of RSV and influenza were different in the southern city.

Influenza virus epidemiological surveillance in Argentina, 1987-1993, with molecular characterization of 1990 and 1993 isolates.

This report describes findings from epidemiological surveillance of influenza virus in two cities in Argentina (Mar del Plata and Córdoba) from 1987 to 1993. It includes information on reporting and serologic characterization of isolated influenza viruses. In addition, determination was made of the nucleotide sequences of the HA1 subunits of five type A (subtype H3) viral strains isolated in the epidemics of 1990 and 1993. The incidence of illness, type of viruses isolated, and H gene sequences were similar to what has been reported from other parts of the world during the same period. The H3 strains isolated in the 1990 and 1993 seasons were somewhat removed in their molecular characteristics from the strains the World Health Organization recommended for vaccines for those years, and appeared closer to the strains recommended for vaccination in subsequent seasons.

An indirect solid-phase microradioimmunoassay for human IgM-anti-IgG (rheumatoid factor).

In order to satisfy the general need for a more precise measurement of the serum concentration of rheumatoid factor (RF) than is presently obtainable with the latex test, we developed a rapid indirect solid phase micro radioimmunoassay for RF determination. The assay involves the binding of IgM-anti IgG (RF), to the polyclonal, native or denatured human IgG dried on the bottom surface of microtiter plates; the amount of antiglobulin bound is then determined by adding 125I-labelled goat anti-human IgM (125I-AHIgM). Variations of reagents and their concentrations, temperatures and incubation times were studied to find the optimal conditions for test sensitivity, specificity and reproducibility. The test has a within day and between day average coefficient of variation of 9 and 15% respectively, showing its advantages over the latex test. The results obtained by studying 100 human sera from patients with positive or negative latex test show that the test should prove valuable in diagnosis and research.

Cytomegalovirus specific IgM and IgG response in humans studied by radioimmunoassay.

An indirect solid phase micro-radioimmunoassay (RIA) was adapted for the measurement of anti-cytomegalovirus class-specific immunoglobulin M (IgM) and immunoglobulin G (IgG). Cytomegalovirus (CMV) antigen (Ag) was added to the wells of microtiter plates and desiccated onto the bottom surface of the wells. Serial dilution of human CMV antisera were added and allowed to react with the Ag. The amount of viral antibody (Ab) was determined by measuring the specific binding of 125I-labeled goat anti-human IgG (125I-AHIgG) and/or IgM (125I-AHIgM). The multiple factors which influence the test were determined. Serial samples of sera from CMV-positive patients showed progressive increases in Ab titers on the basis of specific binding of 125I-AHIgG. The titers of IgM class anti-CMV Ab were also determined with the same sera, and enhancement of the titers was demonstrated when the incubation periods of the first Ag-Ab reaction were extended from 1 to 3 hr. The competition between the different Ig classes of Ab for CMV Ag and the involvement of rheumatoid factor (RF) were investigated. The anti-CMV IgG that may compete with the IgM determination was removed by adsorption of sera with Staphylococcus aureus (Cowan 1). The RF that would cause false anti-CMV IgM results was adsorbed with glutaraldehyde-insolubilized IgG. Our results indicate that this RIA is a practical, specific, and reproducible technique for detection of specific IgG and IgM Ab to CMV.

Properties of the Hong Kong influenza virus. Antigenic relationship of the Hong Kong virus haemagglutinin to that of other human influenza A viruses.

The magnitude of antigenic change of the Hong Kong strains from the earlier influenza A2 strains was compared with previous antigenic changes among the type A viruses. Representative type A strains recovered from man during the years 1933 through 1969 were examined by reciprocal haemagglutination-inhibition, neutralization and neuraminidase-inhibition tests, using antisera produced in chickens. Phenograms or "family trees" were constructed, using numerical taxonomic methods based on cluster analysis of similarity coefficients. By the use of numerical taxonomic methods the inequality of the antigenic relationships among presently recognized classes becomes evident. Antigenic dissimilarities between A0 and A1 strains seen in phenograms constructed from reciprocal haemagglutination-inhibition and neutralization tests were of lower magnitude than dissimilarities between A1 and A2 strains and should not be given equal emphasis. The degree of antigenic dissimilarity between the Hong Kong-like strains and the early A2 strains was even less than that between A0 and A1.The authors stress the need for a new system for identifying and classifying human influenza A strains.