How long after testing positive for influenza does a patient remain positive?

From the Guidelines

Patients typically remain influenza test-positive for approximately 5 days after illness onset, but this duration can vary significantly depending on factors such as age and immune status. The duration of influenza test positivity is influenced by several factors, including the type of test used, the patient's age, and their immune status. According to the study by 1, adults and children are typically infectious from the day before symptoms begin until approximately 5 days after illness onset. However, children can be infectious for a longer period, and very young children can shed virus for <6 days before their illness onset. Severely immunocompromised persons can shed virus for weeks. Key factors to consider include:

• The type of test used, with PCR tests detecting viral RNA for longer periods than rapid antigen tests
• The patient's age, with children and older adults potentially remaining test-positive for longer periods
• The patient's immune status, with immunocompromised individuals potentially shedding virus for extended periods It's also important to note that test positivity doesn't always correlate with contagiousness, as patients are typically most contagious during the early stages of illness when viral loads are highest, as noted in the study by 1. In terms of infection control, guidelines recommend isolation for at least 24 hours after fever resolution without antipyretics, regardless of test status, to minimize the risk of transmission to others.

From the Research

Duration of Influenza Positivity

• The provided studies do not directly address how long a patient remains positive for influenza after testing positive 2, 3, 4, 5, 6.
• However, the studies discuss the duration of influenza-related symptoms and the effectiveness of antiviral treatments in reducing the duration of illness.
• According to the studies, antiviral treatments such as oseltamivir and zanamivir can decrease the median duration of influenza-related symptoms by approximately 1 day if initiated within 48 hours of symptom onset 3.
• The studies also mention that the benefit of treatment is greatest when antiviral therapy is started within 24 hours of symptom onset, and that treatment can decrease the duration of illness by about 24 hours in otherwise healthy patients 2.
• Additionally, the studies discuss the importance of prompt treatment and the potential impacts of outpatient antiviral treatment in reducing influenza-associated hospitalizations 4.

Antiviral Treatment and Symptom Duration

• The efficacy and safety of antiviral treatments such as oseltamivir, zanamivir, and baloxavir marboxil are reported in the literature, with a particular attention toward special populations 5.
• A comparison of the efficacy and safety of oseltamivir and zanamivir in pandemic influenza treatment found that there was no significant difference in efficacy between the two drugs, but temperature normalization was significantly faster in patients taking zanamivir 6.
• The studies suggest that antiviral treatment can reduce the risk of serious complications and decrease the duration of illness, but the optimal duration of treatment and the factors that influence the duration of influenza positivity are not directly addressed 2, 3, 4, 5, 6.