A case-control study conducted in southern Brazil described the first case of triple influenza virus infection, and researchers said their findings indicate that “influenza virus coinfections probably occur more often than has been previously documented.”
“The clinical implications of coinfections with distinct influenza viruses in the respiratory tract is not well understood,” Ana B. G. Veiga, PhD, from the Federal University of Health Sciences of Porto Alegre, Brazil, and colleagues wrote. “Moreover, [influenza A virus] and [influenza B virus] coinfections have been reported only occasionally. The factors that are responsible for mixed influenza virus infection have not been determined; they can be associated with the host’s immune system, virus properties, and other factors.”
The researchers analyzed respiratory tract samples of patients with suspected influenza virus infection who were reported to the Brazilian Health Surveillance System between July 2009 and December 2018.
Patients with more than one influenza A subtype in the same sample or influenzas A and B in the same sample simultaneously were defined a coinfection. The analysis included 76 control patients who had a single influenza A or influenza B infection, according to the study.
Veiga and colleagues identified 19 total coinfection cases, with 18 cases having dual infections. The median age of the dually infected patients was 16 years, and the median age of the control patients was 17 years, the researchers reported.
One case involved coinfection with A(H1N1)pdm09 and A(H3N2), six cases involved coinfection with A(H1N1)pdm09 and influenza B, eight cases involved coinfection with A(H3N2) and influenza B, and three cases involved coinfection with nonsubtyped influenzas A and B. There was one case of triple infection involving A(H3N2), A(H1N1)pdm09, and influenza B.
The coinfections were retrospectively identified in 2009, 2012, 2013, 2014 and 2017. During those years, Veiga and colleagues noted that the frequency of coinfection was less than 0.4% annually. However, 2017 saw an increase in frequency, reaching 1.26%.
“It is noteworthy that 2009 and 2017 had the highest number of influenza virus coinfections in Rio Grande do Sul,” Veiga and colleagues wrote.
In 2009, southern Brazil was affected by the pandemic, which not only increased the number of samples collected but also the chances of detecting possible coinfections, according to the researchers. Then, in 2017, influenza A(H3N2) and influenza B virus both circulated at a high frequency, increasing the risk for coinfection.
According to the study, coinfection was significantly associated with cardiopathy and death compared with single infection. The researchers detected no significant differences between coinfected and monoinfected cases regarding vaccination status, antiviral treatment, timeliness of antiviral use, hospitalization and ICU admission.
“Owing to the cocirculation of [influenza A] subtypes, which is associated with a risk of reassortment and the generation of antigenically novel viruses with epidemic and pandemic potential, coinfections should be considered in surveillance and pandemic preparedness,” Veiga and colleagues wrote. – by Marley Ghizzone
Disclosures: The authors report no relevant financial disclosures.