Rapid Antigen Testing in Influenza Surveillance

Abstract & Commentary

Synopsis: Rapid antigen testing may serve as an early warning system in influenza surveillance.

Source: Wunderli W, et al. Rapid antigen testing for the surveillance of influenza epidemics. Clin Microbiol Infect. 2003; 9:295-300.

With the specter of SARS hanging over the world, we have lost sight of the morbidity and mortality caused by influenza epidemics each year. This article from University Hospital in Geneva, the Swiss Federal Office of Public Health, and Roche Pharma in Switzerland addresses the important question of how useful a rapid antigen test would be in surveillance of influenza epidemics. It also raises the question of how useful such a test would be for diagnostic insights during an outbreak of influenza.

The study seasons were the winter of 1999-2000 and 2000-2001. There was an epidemic of influenza in Geneva for each study period, though the first season was about twice the intensity of the second. More than 200 practitioners participated in the project, under the auspices of the Swiss Sentinel Surveillance Network (SSSN). Influenza virus was isolated at the National Center of Influenza. During the study, 55 practitioners actually sent samples for virus detection by isolation on cell culture (throat and nasal swab), and 198 practitioners sent samples for "near patient" testing, which was an influenza virus antigen. The rapid test used was the INFLUENZA A/B-RAPID TEST provided for the study by Roche Diagnostics. Results were published twice weekly at the influenza study web site, www.influenza.ch.

In the first season, the peak of intensity was seen in the first week of 2000, whereas for the second winter the peak was in the sixth week. There were 39 cases of virus isolation in the first winter at the peak and only about 20 in the second winter. The antigen detection, near patient test lagged slightly behind and was not as sensitive picking influenza out of influenza-like illnesses. The average time for a positive cell culture was 11 days, while the near test results were available 6 days earlier. Note that samples from the same patient were not available for comparison. Nevertheless, the cell culture was more sensitive, 33% vs 26% in the first year and 23% vs 12% in the second year. The sensitivity of the near patient assay increased as the epidemic evolved, suggesting the practitioners were more likely to detect influenza when it was the primary virus causing influenza-like illness.

Comment by Joseph F. John, Jr., MD

The global SARS epidemic has intensified the need for accurate, rapid tests for acute viral illness. Viral antigen detection systems have been around for years, but studies like the present one have not been numerous.

The advantage to the rapid test is that it can be done with minimal laboratory support. Developing countries do not have the restrictions set upon US practitioners, and there is no reason why some of these rapid tests cannot be adapted for office practice. Switzerland is a small but very well-organized country. In such countries, regional laboratories may be able to process rapid testing fast enough to make it useful for public health purposes. It is not hard now to imagine 1 effect of the SARS epidemic being more vigilance of influenza virus outbreaks, perhaps to the extent that person-to-person transmission can be reduced.

Several rapid tests for influenza have been developed but are not widely used globally or in the United States. The Swiss study gives credence to the use of rapid testing for public health purposes and suggests that there may be clinical use, particularly during influenza outbreaks, of using rapid antigen testing.

Dr. John is Chief, Medical Subspecialty Services, Ralph H. Johnson Veterans Administration Medical Center; Professor of Medicine, Medical University of South Carolina, Charleston, SC.