validity of the widal test in the diagnosis of typhoid...

Validity of the Widal Test in theDiagnosis of Typhoid Fever among

Patients in Two General Hospitals inKaduna State, March – July, 2014

NIGERIA FIELD EPIDEMIOLOGY AND LABORATORY TRAINING PROGRAMME

Celestine A. Ameh1, S. Ahmed 2, M. Chori3 C.Benjamin4, S. Shehu2, A. Olayinka2

1. Nigeria Field Epidemiology and Laboratory Training Program

2. Ahmadu Bello University, Zaria, Nigeria

3. Barau Dikko Specialist Hospital, Kaduna , Nigeria

4. Yusuf Dantsoho Memorial Hospital, Kaduna, Nigeria

Introduction

• In 2010, there was an estimated 13.1million incident cases of Typhoid fever(TF) globally

• Africa accounted for 46% of this incidence• In Nigeria, prevalence of TF ranges from

39%-73.9%• Children between the ages of 1-10years

most affected

• In 2010, there was an estimated 13.1million incident cases of Typhoid fever(TF) globally

• Africa accounted for 46% of this incidence• In Nigeria, prevalence of TF ranges from

39%-73.9%• Children between the ages of 1-10years

most affected2

Introduction...2

• Gold standard for diagnosis is bloodculture technique– Time consuming, expensive and technical

• The most common diagnostic approach isthe use of the Widal Test (WT)

• Inconsistency in Widal result from differenthealth facilities (Igharo et al,2012)

• Gold standard for diagnosis is bloodculture technique– Time consuming, expensive and technical

• The most common diagnostic approach isthe use of the Widal Test (WT)

• Inconsistency in Widal result from differenthealth facilities (Igharo et al,2012)

Introduction...3

• Few studies have assessed validity inquantifying the diagnostic value of theWidal test

• We set out to determine the sensitivityand specificity of the Biosystems andSpectrum test kits and the level ofagreement in the results of these two kits

• Few studies have assessed validity inquantifying the diagnostic value of theWidal test

• We set out to determine the sensitivityand specificity of the Biosystems andSpectrum test kits and the level ofagreement in the results of these two kits

Methods

• Study area: Yusuf Danstoho and BarauDikko Specialist Hospital in Kadunametropolis

• Study design: A cross-sectional study• Study population: Febrile patients of all

age group

• Study area: Yusuf Danstoho and BarauDikko Specialist Hospital in Kadunametropolis

• Study design: A cross-sectional study• Study population: Febrile patients of all

age group

Methods...2

• Eligibility criteria: Febrile patients (axilliarytemp > 38º C) with either all or any of thefollowing symptoms: headache, vomitingand abdominal pain;

• Eligible patients who consented toparticipate in the study were systematicallyrecruited

• Eligibility criteria: Febrile patients (axilliarytemp > 38º C) with either all or any of thefollowing symptoms: headache, vomitingand abdominal pain;

• Eligible patients who consented toparticipate in the study were systematicallyrecruited

Methods...3

Sample size determinationSensitivity of Widal test (P) = 50%

Prevalence of typhoid in Borno: 41.2% (Isa et al 2013)

Z score for 95% confidence level: 1.96

Level of precision(d): 5%

n = 384 = No. of infected patients detected

Therefore, Total No. of patients to be recruited = 384/0.42 = 915

(Banoo et al, 2006)

Sample size determinationSensitivity of Widal test (P) = 50%

Prevalence of typhoid in Borno: 41.2% (Isa et al 2013)

Z score for 95% confidence level: 1.96

Level of precision(d): 5%

n = 384 = No. of infected patients detected

Therefore, Total No. of patients to be recruited = 384/0.42 = 915

(Banoo et al, 2006)

Methods...4

• Sampling technique:– Using a daily sampling frame of 200, and a sampling

interval of 5, the first patient was randomly selected.Subsequently, every fifth patient was sampled untilthe sample size was attained

• Study instruments– Patients case files

– Laboratory request forms and worksheets

– A semi-structured questionnaire to assess patientsdemographic profile, antibiotic usage & clinical history

• Sampling technique:– Using a daily sampling frame of 200, and a sampling

interval of 5, the first patient was randomly selected.Subsequently, every fifth patient was sampled untilthe sample size was attained

• Study instruments– Patients case files

– Laboratory request forms and worksheets

– A semi-structured questionnaire to assess patientsdemographic profile, antibiotic usage & clinical history

Methods...5

Laboratory methods:• Blood culture

– All non lactose fermenting (NLF) colonies measuringbetween 2-3mm in size on solid media were identifiedas Salmonella typhi if they fulfilled the followingidentification criteria as outlined:

– Hanging loop test-Motile, Triple Sugar Iron (TSIA)-Alkaline/Acid + Gas (H2S), Urease-Negative, Indole-Negative, Oxidase-Negative, Citrate-Positive

Laboratory methods:• Blood culture

– All non lactose fermenting (NLF) colonies measuringbetween 2-3mm in size on solid media were identifiedas Salmonella typhi if they fulfilled the followingidentification criteria as outlined:

– Hanging loop test-Motile, Triple Sugar Iron (TSIA)-Alkaline/Acid + Gas (H2S), Urease-Negative, Indole-Negative, Oxidase-Negative, Citrate-Positive

A7 See how the laboratory section can be reducedAJII, 3/11/2016

Methods...6

• Widal test– Slide and tube agglutination techniques was carried

out using standard procedure

– Widal test was considered positive if patient Widalagglutinin titre was ≥160 and if a 2 fold raise in titrewas observed in paired sera tested at two weeksinterval from the same patient, otherwise, it isnegative

– Widal test was considered negative if there was noagglutination in the Slide test or if paired sera showedno increase in tube agglutinin titre after 2 weeks

• Widal test– Slide and tube agglutination techniques was carried

out using standard procedure

– Widal test was considered positive if patient Widalagglutinin titre was ≥160 and if a 2 fold raise in titrewas observed in paired sera tested at two weeksinterval from the same patient, otherwise, it isnegative

– Widal test was considered negative if there was noagglutination in the Slide test or if paired sera showedno increase in tube agglutinin titre after 2 weeks

Methods...7

• The result of the tube Widal test wascompared to the blood culture result todetermine the Sensitivity and Specificity ofthe Biosystems and Spectrum Widal testkits

Statistical analysis

• Univariate analysis: Median andproportions

• Validity was calculated using Wilsonsmethod

• Reproducibility of the Widal result of theBiosystems and Spectrum kits wasassessed using Altman’s Standard kappastatistic

• Univariate analysis: Median andproportions

• Validity was calculated using Wilsonsmethod

• Reproducibility of the Widal result of theBiosystems and Spectrum kits wasassessed using Altman’s Standard kappastatistic

RESULTS

Variable Frequency (%)Sex

Male 401(45.1)Female 489(54.9)

Age Group (yrs)< 10 273(30.70

Sociodemographic characteristics of eligiblepatients in Kaduna (2014)

< 10 273(30.7010-19 304(34.2)20-29 107(12.0)30-39 79(8.90)40-49 64(7.2)50-59 29(3.2)>=60 34(3.8)

Median age 16 [Range: 1-91]

Variable Frequency (%)Occupation

Paid employed 249(28.0)

Self employedUnemployed

133(14.9)508(57.1)

Educational status

Sociodemographic characteristics of eligiblepatients in Kaduna (2014)

Self employedUnemployed

133(14.9)508(57.1)

Educational statusNone 262(29.4)

Primary 264(29.7)Secondary 254(28.5)

Tertiary 110(12.4)LGA

Kaduna North 377(42.3)Kaduna South 513(57.7)

Validity of the Widal test using Biosystems andSpectrum Kits at a cut-off value of 1/160 in

Kaduna (2014)Kits Sensitivity

(%)CI (95%) Specificity

(%)CI (95%) PPV CI (95%) NPV CI (95%)

Biosystems

TO 56.3 48.3-63.9 85.8 83.1-88.1 44.7 37.8-51.8 90.6 88.2-92.5

TH 47.0 39.2-54.9 88.3 85.8-90.4 45.2 37.6-53.0 89.0 86.6-91.1Spectrum

TO 53.6 45.7-61.4 85.7 83.0-88.1 43.5 36.6-50.7 90.0 87.6-92.0

TH 41.0 33.5-49.0 87.9 85.4-90.1 41.0 33.5-49.0 87.9 85.4-90.1TO

Reproducibility of the Biosystems and Spectrumwidal kits at a cut-off value of 1/160 in Kaduna

(2014)

Widal Kits

WidalAntibodies

Biosystems Spectrum Kappa 95% CI

Anti TO

Positive 186 190 0.89 0.85-0.92

Negative 704 700Anti TH

Positive 157 151 0.82 0.76-0.86

Negative 733 73917

DISCUSSION

Discussion

• Widal test showed a low sensitivity– Ability to detect those who have Typhoid fever

is low– More than half of the patients diagnosed as

having typhoid actually do not have thedisease

– Low diagnostic value

• Widal test showed a low sensitivity– Ability to detect those who have Typhoid fever

is low– More than half of the patients diagnosed as

having typhoid actually do not have thedisease

– Low diagnostic value

Discussion...2

• Widal test showed a moderate specificity– Ability to detect those who do not have the

disease is moderate– A waste of time and resources– A negative Widal test has little clinical value

• Widal test showed a moderate specificity– Ability to detect those who do not have the

disease is moderate– A waste of time and resources– A negative Widal test has little clinical value

Discussion...3

• Inter kit performance of Widal Kit iscomparable– Observed inconsistency of the Widal test less

likely to be due to kit standardization– Less likely to be due to testing proficiency

• Inter kit performance of Widal Kit iscomparable– Observed inconsistency of the Widal test less

likely to be due to kit standardization– Less likely to be due to testing proficiency

Conclusion

• The Widal test which is an antibody basedtest has a low sensitivity and moderatespecificity

• Low Validity values not due to kitstandardization since kappa statisticshows comparability in test result

• The Widal test which is an antibody basedtest has a low sensitivity and moderatespecificity

• Low Validity values not due to kitstandardization since kappa statisticshows comparability in test result

Recommendation

• Health workers should be encouraged touse more valid tests in the diagnosis ofTyphoid fever

• Utility of new antigen based test should beexplored e.g. Typhidot

• Health workers should be encouraged touse more valid tests in the diagnosis ofTyphoid fever

• Utility of new antigen based test should beexplored e.g. Typhidot

Public Health Action

• Increased sensitization to Clinicians inthese two Hospitals on the outcome of ourfindings and on the need to discontinuewith the use of the Widal test

THANK YOU

Ethical considerations

• Written Informed consent was obtainedfrom all recruited participants

• Ethical approval was granted by the Ethicscommittee of the Kaduna State Ministry ofHealth

• Written Informed consent was obtainedfrom all recruited participants

• Ethical approval was granted by the Ethicscommittee of the Kaduna State Ministry ofHealth

A10 can be a hidden slideAJII, 3/11/2016

Limitations

• Information bias• Low level of Bacterial isolation

– Bactec would have given us a higher isolation

• Information bias• Low level of Bacterial isolation

– Bactec would have given us a higher isolation

A11 can come under discussionAJII, 3/11/2016

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