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Table of Contents
ORIGINAL ARTICLE
Year : 2022  |  Volume : 8  |  Issue : 1  |  Page : 16-19

Positivity of typhidot test in COVID cases: An observational cohort study from the second wave of the pandemic


1 Department of Respiratory Medicine, Santosh Medical College, Lucknow, Uttar Pradesh, India
2 Command Military Dental Centre, Central Command, Lucknow, Uttar Pradesh, India
3 Department of Respiratory Medicine, Santosh Deemed to be University, Ghaziabad, Uttar Pradesh, India

Date of Submission22-Apr-2022
Date of Decision27-Apr-2022
Date of Acceptance30-Apr-2022
Date of Web Publication21-Jul-2022

Correspondence Address:
Prachi Saxena
Department of Respiratory Medicine, Santosh Deemed to be University, Ghaziabad, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/sujhs.sujhs_23_22

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  Abstract 


Introduction: Typhidot has been known to cross-react with a variety of viral illnesses. There has been some communication throwing light on the possible false-positive results in COVID cases, but overall there is a dearth of studies directly investigating the association. This is a small-sized observational cohort study to detect and analyze the association between these two conditions.
Materials and Methods: During a period of 1 month, starting from April 1, 2021, to April 30, 2021, all patients admitted with a Reverse Transcriptase- Polymerase Chain Reaction (RT-PCR)- positive report for SARS-CoV-2 to a nursing home in Ghaziabad were prescribed typhidot immunoglobulin M (IgM) test. Other parameters such as the radiological computed tomography score, hemoglobin levels, total leukocyte counts, serum glutamic-oxaloacetic transaminase, serum glutamic pyruvic transaminase enzyme levels, and the cycle threshold values of the RT-PCR test were recorded. The data thus collected were entered into a structured electronic data collection system and analyzed.
Results: Thirty-seven percent of patients who were admitted with a diagnosis of RT-PCR-positive mild-to-moderate COVID pneumonia were also positive for typhoid IgM antibody. The distribution of this positive typhidot test was equal among both genders and was not found to be significantly associated with any of the other test variables.
Conclusion: Our study reveals the anamnestic response of typhoid IgM antibodies against SARS-CoV-2. A positive typhidot test should not mislead or delay the diagnosis of any other viral respiratory illness.

Keywords: COVID, immunoglobulin M, pneumonia, typhidot


How to cite this article:
Saxena P, Ghosh S, Mahendran C S, Sharma M, Chandra E, Das P, Raj S, Sivaji S. Positivity of typhidot test in COVID cases: An observational cohort study from the second wave of the pandemic. Santosh Univ J Health Sci 2022;8:16-9

How to cite this URL:
Saxena P, Ghosh S, Mahendran C S, Sharma M, Chandra E, Das P, Raj S, Sivaji S. Positivity of typhidot test in COVID cases: An observational cohort study from the second wave of the pandemic. Santosh Univ J Health Sci [serial online] 2022 [cited 2022 Aug 11];8:16-9. Available from: http://www.sujhs.org/text.asp?2022/8/1/16/351571




  Introduction Top


In the tropics, there has always been an overlap of many diseases causing acute febrile illness (AFI). AFI is synonymous with acute undifferentiated febrile illness defined as fevers resolving in 3 weeks lacking any localizable organ-specific signs or symptoms.[1] AFIs are often caused by infectious diseases in tropical, low-resource settings that have the highest burden of febrile illness.[2] The most common causes discovered in the subcontinent include malaria, dengue, scrub typhus, and leptospirosis. In this background, the COVID pandemic added to the diagnostic dilemma of both the patient and the clinician. COVID presented with a myriad of symptoms which were not necessarily involve the respiratory tract alone. Since little was known about this new adversary, the SARS–CoV-2, a battery of investigations were prescribed before finally making a conclusive diagnosis. The typhidot test was one such investigation which was done in a majority of patients, both in inpatient and outpatient settings.

The typhidot test is a rapid diagnostic test which measures both immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies against a 50 kDa outer membrane protein antigen in a miniaturized dot-blot enzyme-linked immunosorbent assay format. The test is considered positive if the IgM is positive and indeterminate if the IgG is positive but IgM negative. Sensitivities ranged from 27% to 100%, and specificities ranged from 38% to 99%, as per the latest study published in 2016.[3]

Typhidot has been known to cross-react with other viral illnesses such as dengue.[4] There has been some communication throwing light on the possible false-positive results in COVID cases, but overall, there is a dearth of studies directly investigating the association between this new viral illness and this commonly prescribed test.[5] Ours is a small-sized observational cohort study to detect and analyze the association between these two conditions.


  Materials and Methods Top


During a period of 1 month, starting from April 1, 2021, to April 30, 2021, all patients admitted with a RT-PCR-positive report for SARS-CoV-2 to a nursing home in Ghaziabad were considered for the study. After taking informed consent, the blood samples of all enrolled patients were sent for typhidot IgM test.

Patient pro formas were filled, taking into consideration other parameters such as the radiological computed tomography (CT) score, hemoglobin (Hb) levels, total leukocyte counts (TLC), serum glutamic-oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT) enzyme levels, and the cycle threshold values (Ct) of the RT-PCR test.

The data thus collected were entered into a structured electronic data collection system.

Statistical analysis

Demographic characteristics and the results of the typhidot test were presented as the median interquartile range for the continuous variables and expressed as absolute values along with/side percentages for the categorical variables. The data were collected and entered into MS 2010. Different statistical analysis was performed using R software version 4.0.2. The one-sample Kolmogorov–Smirnov test was employed to determine whether the data differed from a normal distribution or not. Normally distributed data were analyzed using parametric tests, and nonnormally distributed data were analyzed using nonparametric tests. Descriptive statistics were calculated for the qualitative and categorical variables. Graphical representation of the variable was shown to understand the results clearly and to measure the association for the categorical dataset was analyzed using the Chi-square test. Independent t-test or student t-test was applied to measure the mean difference between the two groups. The correlation was estimated to measure the strength of the relationship between two or more quantitative variables.

If P < 0.05, it was considered statistically significant and if P > 0.05, then it was considered statistically insignificant.


  Results Top


A total of 84 patients admitted with a positive RT-PCR report for SARS-CoV-2 gave consent for the typhidot test. Around 61% were male patients [Figure 1]. The mean age of admitted patients was 50 years. Among all patients close to one-third of the 84 cases demonstrated a significant level of IgM antibodies to typhoid [Figure 2]. The distribution of the positive test was equal among males and females [Figure 3].
Figure 1: Gender distribution of all COVID patients

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Figure 2: Distribution of typhidot test in all COVID patients

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Figure 3: Gender-wise typhidot test output

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On comparing the positive typhidot test with different variables, a positive correlation was found with age, gender, the RT-PCR Ct value, the CT score, Hb, and TLC levels. Negative correlation was observed with SGOT and SGPT values. However, none of these correlations was statistically significant as per the Spearman's rho correlation table [Table 1]. On studying the correlation between other variables, negative association was observed between age and Hb values, and positive association was observed between SGOT and Ct values [Table 2]. These findings show that in our data, advanced age was significantly associated with low Hb levels and lower Ct values were significantly associated with higher SGOT values [Table 2] and [Figure 4].
Figure 4: Significant Spearman's correlation plot

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Table 1: Spearman's rho correlation table with typhidot test

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Table 2: Significant Spearman's correlation table comparing different variables

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  Discussion Top


Dealing with the COVID pandemic proved to be a learning curve for all specialties involved directly or indirectly in the medical field. Making a timely and correct diagnosis of COVID has been of prime importance in managing this new adversary. There is a gamut of unnecessary and nonspecific investigations which tend to cause a loss of crucial time between correct diagnosis and initiation of treatment.

Typhidot is one such investigation which is known to cross-react with a variety of infective diseases such as dengue and tuberculosis. Although there was some communication highlighting the false positivity of typhidot test in COVID patients, we could not find any study evaluating this association in detail. Thus, the aim of our small-sized observational study was to study the correlation between this new disease and this often prescribed investigation.

In our study, we found that 37% of patients who were admitted with a diagnosis of RT-PCR-positive mild-to-moderate COVID pneumonia were also positive for typhoid IgM antibody. The distribution of this positive typhidot test was equal among both genders and was not found to be significantly associated with any of the other test variables. Significant negative association was found between age versus Hb and Ct values of RT-PCR versus SGOT levels. This throws light on the diminishing Hb levels with advancing age and rise in SGOT levels with a fall in Ct values. Both these findings correlate with our existing knowledge of COVID.[6]

Thus, our study reveals the anamnestic response of typhoid IgM antibodies against SARS-CoV-2. A positive typhidot test should not mislead or delay the diagnosis of any other viral respiratory illness. Post the deadly delta wave, the latest drugs and antibodies developed against the SARS-CoV-2 are known to have maximum efficacy within the first 7–10 days of the onset of symptoms. The crucial time involving the initial stages of inflammation and pneumonia in the pathogenesis of SARS-CoV-2 should not be lost due to nonspecific investigations. This observation is pertinent in pandemic situations and resource-limited settings like all developing countries.

However, large-scale studies are required to assess the association of other such investigations and its effect on the diagnosis and management of COVID.


  Conclusion Top


Our study reveals the anamnestic response of typhoid IgM antibodies against SARS CoV 2. A positive typhidot test should not mislead or delay the diagnosis of any other viral respiratory illness.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Bhaskaran D, Chadha SS, Sarin S, Sen R, Arafah S, Dittrich S. Diagnostic tools used in the evaluation of acute febrile illness in South India: A scoping review. BMC Infect Dis 2019;19:970.  Back to cited text no. 1
    
2.
Crump JA, Newton PN, Baird SJ, Lubell Y, Holmes KK, Bertozzi S, et al., editors. Febrile illness in adolescents and adults. In: Major Infectious Diseases. 3rd ed. Washington (DC): The International Bank for Reconstruction and Development / The World Bank; 2017.  Back to cited text no. 2
    
3.
Wijedoru L, Mallett S, Parry CM. Rapid diagnostic tests for typhoid and paratyphoid (enteric) fever. Cochrane Database Syst Rev 2017;5:CD008892.  Back to cited text no. 3
    
4.
Bhatti A, Ali F, Satti S. Cross-reactivity of rapid salmonella typhi IgM immunoassay in dengue fever without co-existing infection. Cureus 2015;7:e396.  Back to cited text no. 4
    
5.
Malik M, Malik MI. Misleading results of typhi dot test in COVID-19 pandemic. Pak J Surg Med 2020;1:e229.  Back to cited text no. 5
    
6.
Canovi S, Besutti G, Bonelli E, Iotti V, Ottone M, Albertazzi L, et al. The association between clinical laboratory data and chest CT findings explains disease severity in a large Italian cohort of COVID-19 patients. BMC Infect Dis 2021;21:157.  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2]



 

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