An under-recognized influenza epidemic identified by rapid influenza testing, southern Sri Lanka, 2013

Influenza accounts for a large burden of acute respiratory tract infections in high-income countries; data from lower-income settings are limited due to lack of confirmatory testing. Consecutive outpatients presenting to the largest tertiary care hospital in southern Sri Lanka were surveyed for influenza-like illness (ILI), defined as acute onset of fever ≥ 38.0°C and cough. Patients were administered a questionnaire and nasal/nasopharyngeal sampling for rapid influenza A/B testing. We enrolled 311 patients with ILI from March to November 2013: 170 (54.7%) children and 172 (55.3%) males. Approximately half (147, 47.3%) tested positive for influenza, but 253 (81.4%) were prescribed antibiotics. On bivariable analysis, symptoms associated with influenza included pain with breathing (P < 0.001), headache (P = 0.005), fatigue (P = 0.003), arthralgias (P = 0.003), and myalgias (P = 0.006) in children and pain with breathing (P = 0.01), vomiting (P = 0.03), and arthralgias (P = 0.03) in adults. Our final clinical predictive models had low sensitivity and fair specificity-50.0% (95% CI: 38.6-61.4%) and 83.2% (95% CI: 73.4-90.0%), respectively, in children and 52.2% (95% CI: 39.9-64.2%) and 81.4% (95% CI: 70.0-89.4%), respectively, in adults. Our study confirms the ability of rapid influenza testing to identify an influenza epidemic in a setting in which testing is not routinely available.