Flu season may be mostly behind us, but a nasty, highly contagious stomach bug is rising. In recent weeks, hikers in Southern California have been hit with norovirus, according to the Pacific Crest Trail Association. Outdoor enthusiasts along the iconic trail aren’t the only ones suffering. Recent wastewater surveillance reveals an upward trend to “high” levels of norovirus across much of the country, with rates currently rising in the Northeast. From Aug. 1 to May 7, the Centers for Disease Control and Prevention’s NoroSTAT program recorded 1,194 outbreaks, compared with 2,534 during the same period the previous year — consistent with past averages. “At the national level, norovirus is still in the HIGH category due to high concentrations over the last 21 days,” Amanda Bidwell, the scientific program manager at WastewaterSCAN, an academic program through Stanford University in partnership with Emory University, said in an email.…