well the interpretation of widal is complicated.it depends on enedemicity of that particular region(local/endemic titre that ranges from 1:20 to 1;80).single test is not confirmatory unless the titre is significantly high(more than 1:160). also demonstration of rising titre seen in next sample given after 7-10days is significant. but it will not be seen if on treatment. Also a transient rise in antibody is seen in other febrile conditions like malaria etc..(provided you have earlier exposed to typhoid bacteria).to say normally individual will not have any circulating antibodies,so no positive titre.titre is seen only in individual exposed to typhoid bacilli,may either suffered from disease or even in subclinical patients & carrier state. In your case as there is positive titre for all i,e. salmonella typhi also paratyphi,whichis most commonly seen if you are immunised by vaccine(TAB).