To evaluate the diagnostic value of Diazo test in typhoid fever, we studied 100 children with Widal or blood culture positive typhoid (study group) and 30 children with fever due to other diseases such as measles, dysentery, malaria and tuberculosis (control group) admitted at Sir Padampat Mother and Child Health Institute, Jaipur. The history, clinical examination and relevant investigations were recorded on a proforma.

Diazo reagent was made fresh each day by mixing 40 parts of solution A and 1 part of solution B.

Solution A: Sulphanilic acid 0.5 g, conc. HCl 5 ml, distilled water 100 ml.

Solution B: Sodium nitrite 0.5 g, distilled water 100 ml. These solutions were pre- pared once every 3 weeks and kept under refrigeration at 4ºC.

The test was performed by gently mixing 5 ml of urine in a test tube to 5 ml of Diazo reagent. Five drops of 30% ammonium hydroxide were then added. The mixture was shaken and the color of the froth noted. A positive reaction consisted of red or pink coloration of the froth, on two consecutive days or more. Any colour except red or pink was considered negative. The test was done on morning sample of urine in all cases daily from the time of inclusion in the study till the patients were discharged. The test was done daily to find out how long it remained positive and whether it becames negative with treatment or following recovery from illness. Of 100 cases of typhoid fever 9% were below age 3 years while the remaining were between 3 and 17 years.

The Diazo test had a sensitivity of 81% and specificity 90% (Table I). Huckstep reported a sensitivity of 80-90%(4). Raman et al. showed a sensitivity of 92% and specificity of 83.3%(5). No other studies have attempted to highlight the usefulness of this test. It is often not possible in clinical practice to submit blood for culture in the first week of a febrile illness before starting antibiotics. Besides, blood culture is not routinely available everywhere. In our study Diazo test became positive from day 5 of fever and remained positive till day 31 of fever. The average duration of test positivity was 6-16 days of fever. We believe that this is a simple bedside test which can be used to diagnose typhoid fever where facilities for blood culture and Widal test are not available.

Table I__Diazo Test in Typhoid Fever

Positive

81

3

Negative

19

27

False positive (%)

False negative (%)

Sensitivity (%)

Specificity (%)

Positive predictive value (%)

Negative predictive value (%)

Likelihood ratio of positive test

Likelihood ratio of negative test

D. Shivpuri,
H.S. Dayal,
D. Jain,Department of Pediatrics,
SMS Medical College,
Sir Padampat Mother and Child Health Institute,
Jaipur, India.
E-mail: [email protected]