Editing Typhoid fever (section)

=== Widal test ===
{{Main|Widal test}}
[[File:Widal Test Slide.jpg|thumb|Widal test card]]
The [[Widal]] test is used to identify specific antibodies in the serum of people with typhoid by using antigen-antibody interactions.<ref>{{Cite journal |last1=Mawazo |first1=Akili |last2=Bwire |first2=George M. |last3=Matee |first3=Mecky I. N. |date=2019-06-05 |title=Performance of Widal test and stool culture in the diagnosis of typhoid fever among suspected patients in Dar es Salaam, Tanzania |journal=BMC Research Notes |volume=12 |issue=1 |pages=316 |doi=10.1186/s13104-019-4340-y |doi-access=free |issn=1756-0500 |pmc=6551910 |pmid=31167646}}</ref>

In this test, the serum is mixed with a dead bacterial suspension of ''Salmonella'' with specific antigens. If the patient's serum contains antibodies against those antigens, they get attached to them, forming clumps. If clumping does not occur, the test is negative. The Widal test is time-consuming and prone to significant false positives. It may also be falsely negative in recently infected people. But unlike the Typhidot test, the Widal test quantifies the specimen with [[titer|titres]].<ref>{{cite book | vauthors = Feasey NA, Gordon MA | chapter = Salmonella Infections | veditors = Farrar J, Hotez P, Junghanss T, Kang G, Lalloo D, White NJ | title = Manson's Tropical Infectious Diseases. | publisher = Saunders Ltd. | date = 2014 | pages = 337–348.e2 | edition = 23rd | doi = 10.1016/B978-0-7020-5101-2.00026-1 | isbn = 978-0-7020-5101-2 }}</ref>