A repeated Widal agglutination test shows an increase from 1:100 to 1:400 in the titers of antibodies to S. typhi O-antigens in the patient's serum. How can the obtained results be interpreted?

Answer options

1. The patient has typhoid fever
2. The patient was previously vaccinated against typhoid fever
3. The patient is an acute carrier of typhoid microbes
4. The patient has a past history of typhoid fever
5. The patient is a chronic carrier of typhoid microbes