An 18-year-old male was admitted with persistent fever for 1 week accompanied by fatigue and anorexia. Physical examination: temperature 39.4°C, pulse 92/min, liver palpable 2 cm below the costal margin, spleen palpable 1 cm below the costal margin. Laboratory tests: WBC 4.0×10<sup>9</sup>/L, neutrophils 62%, lymphocytes 35%, monocytes 3%. Blood culture grew Salmonella typhi. After 5 days of chloramphenicol treatment, the fever subsided. On day 18 of illness, he passed 50g of melena. The period when typhoid fever is most contagious is: