A 35-year-old male agricultural worker from Kerala presents with a 3-day history of fever, severe headache, and myalgia. He has conjunctival suffusion without exudate and normal renal function (creatinine 0.9 mg/dL). Blood culture is positive for a thin, aerobic spirochete. The patient recovers spontaneously within 10 days without jaundice or renal involvement. Which stage of leptospirosis was this patient in when blood culture was performed?