ATLANTA — Negative rapid influenza antigen test results can delay the initiation of antiviral medication for patients with influenza who are critically ill, according to findings presented at ASM Microbe.
“The CDC recommends antiviral treatment as early as possible for people who are very sick with the flu, or who are at high risk of serious complications based on their age or health if they develop influenza,” Kristen Nordlund, CDC press officer, told Infectious Disease News.
However, rapid influenza antigen tests (RIATs) are the only influenza test available at the point of care, and their high rate of false-negative results can potentially delay treatment in patients who are critically ill, researchers said. Preparing for the H1N1 epidemic in 2009, Po-Yen Huang, MD, of the Chang Gung Memorial Hospital in Taoyuan, Taiwan, and colleagues began initiating influenza PCR and virus culture in conjunction with RIAT at their institution. The researchers retrospectively analyzed cohort data from 307 patients admitted to the ICU with laboratory-confirmed influenza from August 2009 to July 2017 to gauge the impact of RIATs on those who were severely ill with influenza.
RIATs were conducted for 259 cases, and about half (49%) were negative. Additional PCR testing was done in 99 of the 126 negative samples, and almost all of these (99%) were positive by PCR, according to the researchers.
Forty-five cases (15%) could not be confirmed by testing upper respiratory tract samples, and researchers said the diagnosis relied instead on testing samples from the lower respiratory tract.
“Lower respiratory tract samples are of importance for diagnosis of severe influenza infection,” Huang said told Infectious Disease News. “Clinicians need to send lower respiratory tract specimens for testing when concerned about influenza infections in appropriate settings.”
They found that patients whose RIAT was negative had a longer stay in the ICU, with a median of 12 days vs. 9 days for those who received a positive RIAT result. They found that treatment was significantly delayed for patients with a negative RIAT, and antiviral medication was not initiated for a median of 1 day vs. same-day treatment for patients with a positive RIAT (P = .01).
Huang and colleagues suggested that physicians are less likely to administer antiviral medication to patients with a negative RIAT, and for critically ill patients with influenza, a negative RIAT can complicate and prolong clinical outcomes compared with the outcomes of a positive test.
“Proper interpretation of a RIAT result is needed for clinical management of hospitalized patients with suspected influenza infection,” Huang said. “Decision-making based on RIAT is strongly discouraged, and prompt empiric antiviral medication is justified in severe respiratory infection.” – by Marley Ghizzone
Huang PY, et al. Abstract 701. Presented at: ASM Microbe 2018; June 7-11, 2018; Atlanta.
Disclosures: Nordlund works for the CDC. Huang reports no relevant financial disclosures.
Editor’s note: This article was updated to indicate that RIATs have a high rate of false-negative results, which could potentially delay treatment in patients with severe influenza. The editors regret the error.