The epidemiology of influenza B in a rural setting in 1977.

An epidemic of influenza B began in January, 1977, in two rural parishes in northeastern Louisiana and quickly spread to involve 29% of their population with clinical influenza. This epidemic was investigated using a standard questionnaire and a random sample of 4.2% of the population. The clinical illness was typical of influenza, with predominant fever, cough, malaise and headache. Gastrointestinal symptoms were part of the clinical syndrome. Rhinitis and diarrhea were significantly more common in children aged five years or less. Clinical attack rates increased with larger household size. The youngest age groups had clinical attack rate of 40--55%, but the elderly had very low attack rates. The direct cost of influenza-like illness during the epidemic averaged almost $30.00 per case. Knowledge of the cost of influenza-like illness and age-specific attack rates should be useful in planning future control efforts for influenza B.