Editing Typhoid fever (section)

== Diagnosis ==
Diagnosis is made by any [[blood culture|blood]], [[bone marrow]], or [[Human feces|stool]] [[cell culture|culture]]s and with the [[Widal test]] (demonstration of [[antibody|antibodies]] against ''Salmonella'' [[antigens]] [[O-somatic]] and [[H-flagellar]]). In epidemics and less wealthy countries, after excluding [[malaria]], [[dysentery]], or [[pneumonia]], a therapeutic trial time with [[chloramphenicol]] is generally undertaken while awaiting the results of the Widal test and blood and stool cultures.<ref name="Sherris">{{cite book | veditors = Ryan KJ, Ray CG |title=Sherris Medical Microbiology |edition=4th |publisher=McGraw Hill |year=2004 |isbn=978-0-8385-8529-0}}</ref>

=== 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>

===Rapid diagnostic tests===
Rapid diagnostic tests such as Tubex, Typhidot, and Test-It have shown moderate diagnostic accuracy.<ref>{{cite journal | vauthors = Wijedoru L, Mallett S, Parry CM | title = Rapid diagnostic tests for typhoid and paratyphoid (enteric) fever | journal = The Cochrane Database of Systematic Reviews | volume = 2017 | pages = CD008892 | date = May 2017 | issue = 5 | pmid = 28545155 | pmc = 5458098 | doi = 10.1002/14651858.CD008892.pub2 | collaboration = Cochrane Infectious Diseases Group }}</ref>

==== Typhidot ====
Typhidot is based on the presence of specific IgM and IgG antibodies to a specific 50[[Dissociation constant|Kd]] OMP antigen. This test is carried out on a cellulose nitrate membrane where a specific ''S. typhi'' outer membrane protein is attached as fixed test lines. It separately identifies IgM and IgG antibodies. IgM shows recent infection; IgG signifies remote infection.<ref>{{Cite journal |last=Mehmood |first=Khalid |last2=Sundus |first2=Ayesha |last3=Naqvi |first3=Iftikhar Haider |last4=Ibrahim |first4=Mohammad Faisal |last5=Siddique |first5=Osama |last6=Ibrahim |first6=Nida Faisal |date=2015 |title=Typhidot - A blessing or a menace |url=https://pubmed.ncbi.nlm.nih.gov/26101507/ |journal=Pakistan Journal of Medical Sciences |volume=31 |issue=2 |pages=439–443 |doi=10.12669/pjms.312.5934 |issn=1682-024X |pmc=4476358 |pmid=26101507}}</ref>

The sample pad of this kit contains colloidal gold-anti-human IgG or gold-anti-human IgM. If the sample contains IgG and IgM antibodies against those antigens, they will react and turn red. The typhidot test becomes positive within 2–3 days of infection.<ref>{{Cite journal |last=Mehmood |first=Khalid |last2=Sundus |first2=Ayesha |last3=Naqvi |first3=Iftikhar Haider |last4=Ibrahim |first4=Mohammad Faisal |last5=Siddique |first5=Osama |last6=Ibrahim |first6=Nida Faisal |date=2015 |title=Typhidot - A blessing or a menace |url=https://pubmed.ncbi.nlm.nih.gov/26101507 |journal=Pakistan Journal of Medical Sciences |volume=31 |issue=2 |pages=439–443 |doi=10.12669/pjms.312.5934 |issn=1682-024X |pmc=4476358 |pmid=26101507}}</ref>

Two colored bands indicate a positive test. A single control band indicates a negative test. A single first fixed line or no band at all indicates an invalid test. Typhidot's biggest limitation is that it is not quantitative, just positive or negative.<ref>{{cite journal | vauthors = Lim PL, Tam FC, Cheong YM, Jegathesan M | title = One-step 2-minute test to detect typhoid-specific antibodies based on particle separation in tubes | journal = Journal of Clinical Microbiology | volume = 36 | issue = 8 | pages = 2271–8 | date = August 1998 | pmid = 9666004 | pmc = 105030 | doi = 10.1128/JCM.36.8.2271-2278.1998 }}</ref>

==== Tubex test ====
The Tubex test contains two types of particles: brown magnetic particles coated with antigen and blue indicator particles coated with O9 antibody. During the test, if antibodies are present in the serum, they will attach to the brown magnetic particles and settle at the base, while the blue indicator particles remain in the solution, producing a blue color, which means the test is positive.{{citation needed|date=June 2022}}

If the serum does not have an antibody in it, the blue particles attach to the brown particles and settle at the bottom, producing a colorless solution, which means the test is negative.<ref>{{Cite web|url=https://www.reszonics.com/wp-content/uploads/2017/04/Reszon-IFU-TYPHIDOT-Rapid-IgG_IgM-combo-2014-04.pdf|title=TYPHIDOT Rapid IgG/IgM (Combo) |website=Reszon Diagnostics International|access-date=14 November 2019}}</ref>