Evaluation of Influenza Statements
Statements b and c are true, while statements a, d, and e are false. The evidence clearly demonstrates that influenza includes types A, B, and C (not just A and B), the transmission period extends from 1 day before symptoms through approximately 5 days after onset in adults, and the classic clinical picture includes fever, headache, myalgia, cough, and sore throat—not primarily gastrointestinal symptoms, and the vaccine does not provide lifelong immunity due to antigenic drift. 1
Statement Analysis
Statement A: FALSE - More Than Two Types Exist
Influenza A, B, and C are three types of influenza viruses that cause epidemic human disease, not just A and B as the statement claims. 1
Influenza A viruses are categorized into subtypes based on hemagglutinin (H) and neuraminidase (N) surface antigens, while influenza B viruses are not categorized into subtypes. 1
Since 1977, influenza A (H1N1), A (H3N2), and influenza B viruses have been in global circulation. 1
Influenza C exists but causes milder disease and is less clinically significant. 2, 3
Statement B: TRUE - Transmission Period Confirmed
Adults are infectious from the day before symptoms begin through approximately 5 days after illness onset, making this statement accurate. 1
The incubation period for influenza is 1-4 days, with an average of 2 days. 1
Children can be infectious for >10 days after symptom onset, and young children can shed virus for <6 days before their illness onset. 1
Severely immunocompromised persons can shed virus for weeks or months. 1
Statement C: TRUE - Classic Clinical Presentation
Uncomplicated influenza illness is characterized by the abrupt onset of fever, myalgia, headache, severe malaise, nonproductive cough, sore throat, and rhinitis—exactly matching this statement. 1
This constellation of constitutional and respiratory symptoms represents the hallmark presentation of influenza. 4, 5
The abrupt onset distinguishes influenza from many other respiratory pathogens, though this feature alone has limited diagnostic accuracy. 5
Statement D: PARTIALLY TRUE BUT MISLEADING - Gastrointestinal Symptoms Not Primary
While the statement includes accurate respiratory symptoms (fever, headache, cough), vomiting and diarrhea are primarily pediatric manifestations, not the defining clinical picture of influenza. 1
Among children, otitis media, nausea, and vomiting are commonly reported with influenza illness, but these are not the primary presenting features. 1
The classic presentation emphasizes respiratory and constitutional symptoms (fever, myalgia, headache, cough, sore throat), not gastrointestinal symptoms. 1
This statement is misleading because it suggests gastrointestinal symptoms are core features when they are actually secondary manifestations primarily in children. 1
Statement E: FALSE - Annual Vaccination Required
The vaccine does NOT provide lifelong immunity—this is fundamentally incorrect due to antigenic drift. 1
Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason for the usual incorporation of one or more new strains in each year's influenza vaccine. 1
Antibody to one antigenic variant of influenza virus might not protect against a new antigenic variant of the same type or subtype. 1
Annual vaccination is necessary because immunity wanes and circulating strains change each season. 1
Clinical Pitfalls to Avoid
Do not rely on clinical symptoms alone to diagnose influenza—reported sensitivities and specificities of clinical definitions for influenza-like illness range from only 63-78% and 55-71%, respectively, compared with viral culture. 1
The positive predictive value of fever, cough, and acute onset was only 30% for influenza in older nonhospitalized patients. 1, 5
Laboratory confirmation through viral culture, RT-PCR, or rapid diagnostic testing is essential for accurate diagnosis during influenza season. 5
Remember that children present differently than adults—they can have gastrointestinal symptoms, febrile seizures (up to 20% of hospitalized children), and can shed virus for longer periods. 1