Fever is typically considered part of the influenza-like illness in hemagglutinin type 1 and neuraminidase type 1 (H1N1/09) influenza. We assessed the proportion of patients that did not have fever as part of their illness prior to hospital presentation. We assessed the role of fever on the delay in hospital presentation, diagnosis, and treatment of these patients.


We performed a retrospective analysis of all hospitalized adult patients with laboratory-confirmed pandemic H1N1/09 at a tertiary care center in the United States from June 1 to December 31, 2009.


Fifty-six of 135 study patients (42%) had no fever; 31 (23%) required intensive care unit (ICU) admission, and 9 (7%) died. Those without fever had higher Charlson index (P = 0.01), significantly longer time to hospital presentation (median 4 vs 2 days, P < 0.001), longer time to treatment since the onset of illness (median 5 vs 2 days, P = 0.001), and were more frequently in an ICU (P = 0.01). After adjustment for age (<40 vs ≥40) and Charlson index (0, 1–2, ≥3), patients without fever had significantly increased likelihood of late hospital presentation (>2 days from the onset of illness) (P = 0.001) and also had increased likelihood of ICU stay (P = 0.05).


Forty-two percent of patients with laboratory-confirmed H1N1/09 did not have fever as part of their illness prior to hospital presentation. Patients without fever had delayed presentation to the hospital and thus experienced delayed treatment. Journal of Hospital Medicine 2013. © 2012 Society of Hospital Medicine