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Rapid Influenza Test Helps Identify Low-Risk Febrile Infants

A positive rapid influenza test result predicted low risk for serious bacterial infection in febrile infants younger than 3 months.

Strategies for evaluating febrile infants younger than 3 months commonly use laboratory markers to identify patients at low risk for serious bacterial illness (SBI). In a prospective multicenter study, investigators in Spain evaluated whether rapid influenza tests can help identify low-risk patients. During the 2003–2008 influenza seasons, the investigators enrolled 381 infants younger than 3 months (22% aged 28 days) with fever 38°C from an unknown source who were evaluated with blood culture and rapid influenza tests. Patients who had been treated previously with antibiotics were excluded.

Overall, 3 of 113 patients (2.6%) with positive rapid influenza test results had SBI, compared with 47 of 268 patients (17.5%) with negative results. All SBIs in the positive group were from a urinary source. Blood cultures were positive in 0% of patients with positive rapid influenza test results, compared with 8 patients (3%) with negative rapid influenza test results (Streptococcus agalactiae in 4 patients, Neisseria meningitidis in 2, Streptococcus pneumoniae in 1, and Staphylococcus aureus in 1).

Comment: Historically, febrile infants younger than 1 month have been the most difficult to risk stratify. Unfortunately, these authors did not analyze the results by age, making the generalizability of these findings to that higher-risk, youngest age group unclear. However, when these results are coupled with those from previous studies that have demonstrated a low risk for bacteremia in infants with an identifiable viral source of fever, incorporating rapid influenza tests into risk stratification algorithms seems reasonable. Although rapid influenza tests have variable sensitivity, for well-appearing infants between ages 1 and 3 months with positive rapid influenza test results, urine analysis and culture are sufficient to exclude bacteremia. Caution: These investigators looked at seasonal influenza and not 2009 pandemic H1N1 influenza, which has been associated with higher rates of concomitant bacterial pneumonia.

— Katherine Bakes, MD

Published in Journal Watch Emergency Medicine November 13, 2009

Citation(s):

Mintegi S et al. Rapid influenza test in young febrile infants for the identification of low-risk patients. Pediatr Infect Dis J 2009 Nov; 28:1026.

• Medline abstract (Free)