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ATLANTA -- Patients with severe influenza who had a negative rapid influenza antigen test (RIAT) had a significantly longer length of stay in the ICU compared with patients who tested positive, a researcher said here.

ICU length of stay was a median of 12 days for patients who tested negative for influenza via RIAT compared with 9 days for patients who tested positive (P<0.001), reported Po-Yen Huang, MD, of Chang Gung University in Taiwan, and colleagues.

Moreover, nearly half of patients with laboratory-confirmed influenza who were admitted to the ICU tested negative with the RIAT, they stated in a a at the ASM Microbe meeting.

Huang's group said that since the 2009 H1N1 influenza epidemic, the hospital had encouraged their physicians to perform an influenza PCR test at the same time as a RIAT.

They examined a cohort of patients with laboratory-confirmed influenza who were admitted to the ICU over the course of an almost 100-year period (August 2009 to July 2017). Of the 259 cases where a RIAT was performed, 126 were negative.

Researchers looked at these 126 negative cases compared with the 133 positive cases. The overall median age of patients was similar (age 52 to 53), and about 60% to 62% were men. There were no significant differences in underlying conditions between the two groups with the exception of malignancy (cancer), which was significantly higher in the patients who tested positive for influenza via RIAT.

Of the 126 negative test results, PCR testing was checked for 99 of these cases and 98 of 99 were PCR-positive, the authors noted.

When examining virus type, patients testing negative were significantly more likely to have influenza A (H1N1) than patients testing positive, though there was no difference in the other strains of influenza.

Huang told 名媛直播 that the most significant outcome was the difference in ICU length of stay, but that "we don't know why and we're still looking into it."

There was no significant difference in other primary outcomes, such as in-hospital mortality rate, 30-day mortality rate, or median length of stay.

But all secondary outcomes were significant. There were significant differences in the portion of patients receiving antiviral therapy (98% in negative test group versus 92% in positive test group, P=0.036). Antiviral medication (Tamiflu) was "significantly delayed" in the negative testing group (1 day versus 0 days in positive testing group, P=0.01).

Huang also noted that 45 of 307 cases (15%) had either negative results of all upper respiratory tract samples tested (RIAT, PCR, or virus culture) or no evidence of upper respiratory tract testing at all, and these 45 cases "were diagnosed with lower respiratory tract samples."

The authors added that lower respiratory tract samples "are important and clinicians should send [lower respiratory tract] specimens for the diagnosis of severe influenza infection."

"We want to advocate that decision-making based on the rapid test in this particular population is not suggestive," Huang said. "Complementary use of antiviral therapy is needed if physicians think there is an influenza infection, even if the test is negative."

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