The epidemiology of influenza in California, 1968-1973.

Influenza is one of the most common acute febrile respiratory diseases in adults. Epidemics caused by influenza viruses occur every few years. When such epidemics are in progress, the medical community, the general public and the news media seek information regarding the presence, spread and severity of influenza. The methods and findings of the Influenza Surveillance System in California for the years 1968 through 1973 should be of interest generally. This period spans the total California experience with the type A Hong Kong variant (A/Hong Kong/1/68 [H(3)N(2)]), and the first appearance of the English strain of type A influenza virus (A/England/42/72 [H(3)N(2)]). The surveillance of influenza during this period showed that there were major epidemics in Calfornia only during the state's first experience with the type A Hong Kong variant in 1968-69, and with the English strain in 1972-73. Problems and limitations in influenza surveillance do exist. Nonetheless, the major surveillance indices used (school absenteeism, laboratory data and deaths from pneumonia and influenza) are reliable and sensitive indicators of general trends of influenza virus activity. These indices are most useful in comparing the relative severity of influenza epidemics. However, since these indices usually lag several weeks behind the occurrence of disease, this lag must be considered in making estimates of current incidence trends based on these indices.

Association of group B coxsackie viruses with cases of pericarditis, myocarditis, or pleurodynia by demonstration of immunoglobulin M antibody.

Tests for immunoglobulin M (IgM) antibody to group B coxsackieviruses were performed on sera from 259 patients with a clinical diagnosis of pericarditis, myocarditis, or pleurodynia on whom there were no definitive serological or virus isolation findings to establish a viral etiology, and on 259 "control" patients with clinical diagnoses of viral or mycoplasmal pneumonia or pneumonitis. IgM antibodies to coxsackievirus types B1, B3, B4, B5, and B6 were detected by a micro-immunodiffusion technique, and antibodies to virus type B2 were detected by reduction of neutralizing antibodies with ethanethiol. Of the patients with pericarditis, myocarditis, or pleurodynia, 27% (70) had IgM antibody to group B coxsackieviruses, as compared with 8% in the control group. On retrospective review of the clinical diagnosis, some of the patients in the control group with IgM antibody were found to have had additional clinical findings which could be attributed to a coxsackievirus infection. Coxsackievirus IgM antibody was demonstrable in 30% of 113 patients in the study group for whom virus isolation had been attempted with negative results. The presence of coxsackievirus IgM is discussed in relation to the time of serum collection, age of the patients, and month of onset of illness.

The need for routine rubella antibody testing of women.

Results of rubella antibody tests performed by the California State Viral and Rickettsial Disease Laboratory on blood specimens collected in 1968 and 1969 from school children and women of childbearing age showed a slightly lower prevalence of rubella antibody in California than reported from most other areas of the United States. Among women of childbearing age, rubella hemagglutination-inhibition (hi) antibody was found in 72 percent of those tested in California compared with 80 percent to 90 percent in other areas of the country. Rubella antibody testing services offered by the State Virus Laboratory included situations in which a pregnant woman was exposed to a suspected case of rubella. It was shown that very few of these exposures constitute a significant risk to the fetus as most of the women already possessed antibody to rubella from past infection and in many instances the exposures were not to actual cases of rubella. The results of this study emphasized the urgency of obtaining blood specimens from pregnant women as soon as possible after exposure to rubella or development of symptoms of rubella. The urgency and anxiety attending these situations can largely be obviated if routine rubella antibody testing of women is carried out prior to pregnancy or at the first prenatal visit.

Serology of rubella. Comparison of fluorescent antibody, complement fixation and neutralization tests for diagnosis of current infections and determination of sero-immunity.

Neutralization, complement fixation (CF) and indirect fluorescent antibody (FA) assays for rubella virus were compared for sensitivity in the serologic diagnosis of infection, for demonstrating antibody in the sera of infants with suspected rubella syndrome, and in the detection of antibody elicited by past infection (determination of immunity status). The combination of CF and FA tests was shown to be the most useful for serologic diagnosis of infection, largely eliminating the need for the slower and more cumbersome interference neutralization test.Neutralizing antibodies were found to appear rapidly in the course of infection, antibodies demonstrable by immunofluorescent staining appeared slightly later, and CF antibodies were rarely demonstrable in sera collected earlier than 14 days after onset of illness. Antibodies detected by all three techniques showed good correlation in infants with clinical evidence of rubella syndrome and corresponding maternal sera. The indirect FA technique compared favorably with the neutralization test for the detection of antibody elicited by past infection (determination of immunity status) and offered distinct advantages in ease of technical performance and more rapid results. In both current and past infections, FA titers tended to be higher than neutralizing antibody titers.