• Home
  • Tool
  • Results
  • About
  • Methodology
    •

    Multiplier to estimate medically unattended mild/moderate flu cases

    Mild and moderate flu cases are the most likely to be missed by traditional disease surveillance systems. Flu presents with similar symptoms to many other respiratory diseases, including fever and respiratory symptoms, making it difficult to distinguish between them. People with mild and moderate illness may not seek diagnosis or care for their illness, and in some instances, symptoms may be so mild that they are not recognized as an illness. Without a clinical or laboratory diagnosis, these cases are not detected or reported.

    The Flu Tool applies a multiplier to extrapolate from medically attended mild/moderate flu cases in order to generate an estimate for the number of medically unattended mild/moderate cases. Default values are pre-filled below. You may use the default values or edit, as needed, to reflect your hospitalization estimates. If you choose to enter a custom multiplier, you must also enter confidence intervals.

    These estimates are based on limited underlying data, but they may be useful in understanding the number of mild/moderate illnesses potentially missed by surveillance systems.

    Do you want to include a multiplier to estimate mild/moderate flu cases that were not medically attended?

    Please fill in all the necessary fields to continue.

    More about the default multipliers

    Estimating the number of non-medically attended influenza cases is a challenge. Most influenza cases do not seek care for their disease for a variety of reasons, including that symptoms may be mild enough not to meaningfully impact daily life; a lack of access to medical care; and use of care modalities that are not integrated into traditional disease surveillance systems, such as religious leaders, natural healers, or self-care at pharmacies. Medically unattended cases, by definition, do not seek care for their disease, and therefore, do not have clinical or laboratory diagnoses. Because influenza’s clinical presentation is very similar to many other common respiratory diseases, it is extremely difficult to distinguish between diseases in the absence of diagnostic tests.

    Research studies and data corresponding to influenza medical attendance are limited, generally based on small study populations that are not representative of most settings. Much of the available data rely on self-reported symptoms, using influenza-like illness (ILI) case definitions, which could apply to a broad scope of respiratory diseases (i.e., as opposed to specifically influenza). Further study is needed to improve our understanding of care-seeking behavior specific to individuals infected with influenza.

    The default estimates are based on data from 4 studies, listed below.

    • Taylor S, Lopez P, Weckx L, et al. Respiratory viruses and influenza-like illness: epidemiology and outcomes in children aged 6 months to 10 years in a multi-country population sample. J Infect. 2017;74(1):29-41. doi:10.1016/j.jinf.2016.09.003
    • Hunger V, Shapiro A, Chawla D, et al. Characterization of influenza-like illness burden using commercial wearable sensor data and patient-reported outcomes: mixed-methods cohort study. J Med Internet Res. 2023;25:e41050. doi:10.2196/41050
    • Hayward AC, Fragaszy EB, Bermingham A, et al. Comparative community burden and severity of seasonal and pandemic influenza: results of the Flu Watch cohort study. Lancet Respir Med. 2014;2(6):445-454. doi:10.1016/S2213-2600(14)70034-7
    • Chawla D, Benitez A, Xu H, et al. Predictors of seeking care for influenza-like illness in a novel digital study. Open Forum Infect Dis. 2022;10(1):ofac675. doi:10.1093/ofid/ofac675

    How would I calculate my own multipliers?

    Community-based surveys, including routine diagnostic testing or self-reporting on influenza-like illness and care-seeking behavior, can provide information regarding the total community incidence of influenza and the proportion of people with flu who seek medical care for their disease. It is important to remember that influenza-like illness (ILI) is not the same as laboratory-confirmed influenza infection or disease, and case definitions will overlap with other diseases.