ACMT COVID-19 Web Series FAQs

Co-infection with different viruses certainly can occur, and infection with either SARS-CoV-2 or the circulating influenza viruses can increase the likelihood of secondary bacterial infections or other complications, particularly in the elderly and in those with underlying cardiovascular and respiratory health conditions.

Available data indicates that the 2019-2020 influenza activity dropped off much more quickly in late February to March 2020 than typically seen in prior years. Some of this drop-off was attributable to less testing and fewer clinic visits as many individuals and medical practices shut their doors. However, the positivity rate of those tested also decreased, and this was seen in other Northern Hemisphere countries as well – indicating a more rapid termination to the flu season than typically seen. In addition, data from Southern Hemisphere countries this year (covering April – July) indicated a very, very low level of influenza activity during their winter season. The proposed rationale for these findings is the impact of community-wide measures to control SARS-2-CoV-19 transmission (although unfortunately, the data thus far does not distinguish the relative impact of social distancing, use of face coverings, better hand hygiene, business restrictions/lockdowns, etc.).

REFERENCES:

Dadong Li, Donna M Wolk, Michael N Cantor, Comparing Clinical Characteristics of Influenza and Common Coronavirus Infections Using Electronic Health Records, J Infect Dis 2020; jiaa626, https://doi.org/10.1093/infdis/jiaa626

Kuo S, Shih S, Chien L, Hsiung CA. Collateral Benefit of COVID-19 Control Measures on Influenza Activity, Taiwan. Emerg Infect Dis 2020;26(8):1928-1930. DOI: https://dx.doi.org/10.3201/eid2608.201192

Olsen SJ, Azziz-Baumgartner E, Budd AP, et al. Decreased Influenza Activity During the COVID-19 Pandemic — United States, Australia, Chile, and South Africa, 2020. MMWR Morb Mortal Wkly Rep 2020;69:1305-1309. DOI: http://dx.doi.org/10.15585/mmwr.mm6937a6

Soo R, Chiew CJ, Ma S, Pung R, Lee V. Decreased Influenza Incidence under COVID-19 Control Measures, Singapore. Emerg Infect Dis 2020;26(8):1933-1935. DOI: https://dx.doi.org/10.3201/eid2608.201229

Certainly, influenza vaccination is recommended for all individuals over the age of 6 months, with recommendations to get vaccinated as soon as possible (ideally, October through December). Effectiveness in preventing illness can vary (often ~50%), but reduced severity of illness may also be provided. Flu vaccine should be deferred for symptomatic COVID-19 patients for 10 days after onset of symptoms and free of fever without antipyretics for 24 hours, and demonstrating improvement of any COVID-related symptoms. This will result in a better likelihood of an appropriate immune response, and will also avoid potential confusion regarding subsequent symptom development. Please refer to current CDC recommendations at https://www.cdc.gov/vaccines/pandemic-guidance/index.html

REFERENCE:

CDC. Interim guidance for routine and influenza immunization services during the COVID-19 pandemic. https://www.cdc.gov/vaccines/pandemic-guidance/index.html

No. Although it is estimated that more than 10% of the U.S. population is infected by influenza viruses each year (varying widely by predominant strain), influenza is less durable and less transmissible than is the SARS-CoV-2 virus. In addition, influenza is more likely to be transmitted by symptomatic individuals, while a large minority of COVID-19 cases (varying by demographics and individual characteristics) occur as a result of asymptomatic or pre-symptomatic spread.

REFERENCES:

CDC. Influenza (Flu): https://www.cdc.gov/flu/about/burden/2019-2020.html

Savvides C, Siegel R. Asymptomatic and presymptomatic transmission of SARS-CoV-2: a systemic review. medRxiv. Preprint 2020 Jun 17: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7310638/pdf/nihpp-2020.06.11.20129072.pdf

WHO. Influenza: Influenza updates. https://www.who.int/influenza/surveillance_monitoring/updates/en/

The symptoms caused by these respiratory viruses overlap greatly. There are some differentiating features, as listed below, but these may not be sufficient to base individual treatment or public health policy decisions:

• Influenza incubation period is typically shorter (1-4 days, median 2-3 days) vs COVID-19 (2-14, median 4-5 days)
• Progression to severe disease is earlier with influenza (typically in first week), instead of during 2nd or 3rd week with COVID-19
• Severe disease is more common in younger children with influenza than with COVID-19
• Viral shedding period is shorter by a few days with influenza than with COVID-19
• Diarrhea is more common in children with influenza, as opposed to occurring in any age group with COVID-19
• Abnormalities with taste or smell is more common with COVID-19
  
  

Perhaps most importantly, a vaccine for influenza is available every year, produced based on information of strain prevalence, while the vaccines cleared through the FDA Emergency Use Authorization (EUA) for COVID-19 prevention will have limited availability (healthcare workers and some high-risk populations in December/January, and general availability in the spring of 2021). Due to the current pandemic, identification of the offending virus(es) is important, emphasizing the importance of testing strategies (see next FAQs).

REFERENCES:

CDC: Influenza (Flu). Similarities and differences between influenza (Flu) and COVID-19.  https://www.cdc.gov/flu/symptoms/flu-vs-covid19.htm

WHO: Influenza: Influenza updates. https://www.who.int/influenza/surveillance_monitoring/updates/en/

A number of tests are available using different technologies, respiratory secretion source (nasopharyngeal swab is generally preferable to throat swab, while more invasive sampling of lower respiratory tract – e.g., bronchoalveolar lavage specimen – may be needed in severely ill immunocompromised patients), and collection material (e.g., transport media required for viral culture). Some of these tests are uni-plex (only identifying specific influenza viruses), while others are multi-plex (identifying both influenza and SARS-CoV-2, in addition to other respiratory pathogens). Complexity of testing, turn-around time, sensitivity and specificity, as well as more detailed identification (e.g., influenza A strains) vary greatly. Rapid tests including point-of-care assays typically focus on antigen detection, while more sensitive tests detect nucleic acid sequences (e.g., RNA). The tables below provide some comparisons:

[Listing of particular assays is not to be taken as an endorsement of any particular product. This listing is just to provide an example of the wide range of available testing options under the FDA EUA as of November 2020.]

REFERENCES:

CDC. Influenza: Information for clinicians on influenza virus testing. https://www.cdc.gov/flu/professionals/diagnosis/index.htm

Covalciuc KA, Webb KH, Carlson CA. Comparison of four clinical specimen types for detection of Influenza A and B viruses by optical immunoassay (FLU OIA test) and cell culture methods. J Clin Microbio 1999;37(12):3971-3974. https://jcm.asm.org/content/jcm/37/12/3971.full.pdf

NIH: National Institute of Allergy and Infectious Diseases. Influenza diagnosis. https://www.niaid.nih.gov/diseases-conditions/influenza-diagnosis

Guidance may change as the flu season progresses, however certain principles will hold true.

• It is reasonable to base clinical testing on the results of national and regional surveillance testing results – updated weekly by the CDC and WHO.
• In general, analytical testing should be considered when a test result will influence management. Management issues include:
  • Treatment decisions (e.g., use of antivirals)
  • Isolation decisions (e.g., returning a patient who does not need acute hospitalization to congregate settings such as long-term care facilities, correction or detention centers).
• Viral cultures (requiring more than 3 days for results) or serologic testing of blood (requiring acute and convalescent testing for proper interpretation) are not recommended in the acute management of individual patients.
  
  

In the outpatient setting, rapid influenza molecular assays are recommended over rapid influenza antigen detection tests because of the higher sensitivity of the former. If the latter are used, interpretation of positive results during low prevalence (or negative results in 

For hospitalized patients, RT-PCR or other influenza molecular assays are recommended if available. Multiplex assays are most useful, particularly in immunocompromised patients where multiple serious infections and atypical presentations are more common. 

REFERENCE:

Uyeki TM, Bernstein HH, Bradley JS, Englund JA, File TM Jr., et al. Clinical practice guidelines by the Infectious Diseases Society of America: 2018 update on diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza. Clin Inf Dis 2019;68(6):e1–e47. https://doi.org/10.1093/cid/ciy866

Early treatment of hospitalized influenza patients (within 6 hours of presentation) with oseltamivir has been associated with decreased length of stay in observational studies. In general, for hospitalized patients, oral oseltamivir (or intravenous peramivir if GI absorption very compromised) is indicated. For outpatients, any of the currently approved neuraminidase inhibitors or baloxavir may be used if needed and begun within 48 hours of symptom onset (although lack of information regarding pregnancy-associated risks with baloxavir and potential developing drug resistance may limit its use). It should be noted that none of these antivirals are considered effective against SARS-CoV-2.

REFERENCES:

CDC. Influenza (Flu): Influenza antiviral medications: summary for clinicians. https://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm

Uyeki TM, Bernstein HH, Bradley JS, Englund JA, File TM Jr., et al. Clinical practice guidelines by the Infectious Diseases Society of America: 2018 update on diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza. Clin Inf Dis 2019;68(6):e1–e47. https://doi.org/10.1093/cid/ciy866