Typhoid investigation of choice in 1st week

(A) Blood culture # Typhoid investigation of choice code 'BASU'> 'B' i.e. Blood culture in the first week (Better is Bone Marrow culture)> 'A' i.e. Antibodies (Widal) in the second week> 'S' i.e. Stool culture in the third week> 'U' i.e. Urine culture in the 4th week> Widal test shows diagnostic titre for S. typhii usually after 7 to 10 days of the illness - 2nd week> Positivity with Widal test is maximum in third week.> Widal - The agglutinins tested by the Widal test appear by the end of the first week. The titre increases steadily till the third or the fourth week, after which it declines gradually.> Maximum titre is found in third week.> Blood culture- They are positive in approximately 90% of cases in the first week of fever, 75% of cases in the second week, 60% in the third week and 25% thereafter till the subsidence of pyrexia. Test of choice in first week.> Stool culture - Salmonellae are shed in the faeces throughout the course of the disease and even in convalescence, with varying frequency. So a positive fecal culture may occur in carriers as well as in patients. Thus the test is not very useful for a recent infection.> Urine culture - Salmonellae are shed in the urine irregularly and infrequently. Cultures are generally positive only in the second and third weeks and then only in about 25% of cases.