A 26-year-old male presents with sudden onset of fever, chills, headache, and myalgia for 3 days after harvesting rice. Physical exam: temperature 38.6°C, conjunctival congestion, heart rate 90/min, clear lungs. Initially treated as "upper respiratory infection," but symptoms persisted. Laboratory tests: WBC 21.6×10⁹/L (neutrophils 90%), microscopic agglutination test titer 1:400. Diagnosed with leptospirosis. After intramuscular penicillin 800,000U and streptomycin 0.5g, the patient develops chills, high fever, headache, dyspnea, and BP 86/60 mmHg within 30 minutes. The diagnosis and management are: