Published research has suggested that early antiviral treatment of pregnant H1N1 patients can improve outcomes. In a Center for Disease Control and Prevention (CDC) surveillance population of 788 pregnant influenza patients with disease onset between April and August 2009, the 384 with data on timing of antiviral treatment were observed to have significantly higher risk of adverse outcomes with later treatment ('intermediate', i.e. 3-4 days, n=84; 'late', i.e. > 4 days: n=81) than with early treatment (< 2 days: n=219). Compared with those given early treatment, those given intermediate treatment had almost 10 times the risk of death, and those given late treatment, more than 50 times. Intensive Care Unit (ICU) admission showed more than a 2-fold risk elevation with intermediate treatment and a six-fold elevation with late treatment, Respective elevations in risk of need for mechanical ventilation were almost 4-fold and more than 12-fold. The authors noted that the reason for treatment delays in this population are unknown, but could include reluctance on the part of clinicians and patients to expose the fetus to antiviral medications, as well as use of rapid influenza tests, which have shown low (10%-70%) sensitivity for H1N1.