Infectious Diseases

What IS NS1?

• NS1 tests detect the non-structural protein NS1 of dengue virus. This protein is secreted into the blood during dengue infection.
• NS1 tests have been developed for use in serum. Most of these tests use synthetically labeled antibodies to detect dengue NS1 protein.

specimen :

Serum

Interpretation of results:

• A positive NS1 test result confirms dengue virus infection without providing serotype information.
• A negative NS1 test result does not rule out infection. 

Specimen Type

Serum

Time:

7-10 days of fever

Interpretation of the widal test:

1. The highest dilution of the serum is noted where there is agglutination.
2. If it ends at 1:320, then that is the titer.
3. The Widal test interpretations:
   

   The titer of the antibody	Interpretations of the Widal test
   O-antigen = >1:160	Active infection
   H-antigen = >1:160	Past infection or immunized
   Rising titer = 1:40 to 1:80 to 1:160	Diagnostic

O-antigen

1. Antigen-O will be positive in the acute stage, and the titer will be more than 1:160.
2. O-antigen appears early and also disappears early.

H-antigen

1. H antigen rises late and disappears late.
2. It is positive in the recovery stage.

Vi-antigen

1. This is an indicator of the carrier stage.

The false-positive test:

1. It may be seen due to cross-reacting infections, including malaria.

For Nonmedical (non-specialist) person explanation of Widal test (Enteric fever):

1. Please advise the Widal test if the fever persists for more than 5 days and is constant. It does not touch the normal level.
2. The titer of O antigen 1:40 is considered negative.
3. Just see the O antigen titer if it is 1:160, indicating Enteric fever.
4. If the O antigen is 1:80, repeat the test after 5 to 7 days, and now if the titer is 1:160, the rising titer again indicates acute infection.
5. While H antigen does not indicate acute infection or acute enteric fever.