Honolulu—Routine use of the rapid flu test does not undermine influenza surveillance, as some public health professionals have feared. In fact, investigators from the Hawaii State Department of Health (HDOH) who studied the impact of incorporating the rapid flu test into their state’s influenza surveillance program found that the test actually enhanced surveillance.[1]

Beginning in the fall of 1999, the rapid flu test was offered to all licensed physicians in Hawaii for simultaneous use with influenza cultures. During the next two flu seasons, there was more than a fivefold increase in the number of cultures submitted to the HDOH and nearly a tenfold jump in the number of physicians who submitted at least one culture. There was also a marked rise in the number of influenza isolates obtained by the HDOH.

“This shocked us,” admitted lead investigator Paul V. Effler, MD, State Epidemiologist at the Honolulu-based HDOH. The dramatically greater participation in the surveillance program after the rapid test’s introduction suggests that the test holds great appeal to physicians, he told RESPIRATORY REVIEWS. The ability to obtain a broader sample of circulating influenza strains aids vaccine development and the detection of novel strains that may become pandemic, he stressed.

FOUR FLU SEASONS WERE STUDIED

The study covered the four consecutive flu seasons between 1997 and 2001. The rapid test was available during the last two of those seasons. In the first two flu seasons, culture submissions for influenza detection totaled 306 and 396; in the last two seasons, they totaled 1,112 and 2,196. The numbers of physicians who submitted at least one culture in those four seasons were 25, 34, 196, and 327, respectively. The numbers of influenza isolates obtained were 73, 44, 137, and 491, respectively.

NO CHANGE IN FLU SEVERITY

The greater number of culture submissions in the second two flu seasons could have been due to a rise in influenza-like illness, acknowledged the investigators. However, their surveillance suggests that influenza activity in Hawaii did not markedly change during the four seasons studied.

Furthermore, published reports from the Centers for Disease Control and Prevention indicate that influenza activity was similar during most of the study period; if anything, it decreased in the final flu season.

In this study, the rapid test had a positive predictive value of 51% and a negative predictive value of 84%, noted the investigators. They cautioned, however, that their study was not designed to evaluate the rapid test; thus, their results may not reflect the test’s performance in other settings.

They hope to use the rapid test to better target their influenza surveillance and thereby obtain a greater number of isolates. Such a strategy early in the flu season should help them assess whether that year’s vaccine contains the correct strains; later in the flu season, it will help them determine the composition of the following year’s vaccine.

—Timothy Begany