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ORIGINAL ARTICLE Table of Contents  
Ahead of print publication
Test positivity rate, contact history, and vaccination status of COVID-19 among patients visiting flu corner (fever clinic) of a tertiary care health center of Karnataka: A prospective longitudinal study

 Department of Community Medicine, Shimoga Institute of Medical Sciences, Shivamogga, Karnataka, India

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Date of Submission23-Jul-2022
Date of Decision07-Oct-2022
Date of Acceptance12-Oct-2022
Date of Web Publication02-Dec-2022


Background: In December 2019, patients with viral pneumonia-like illnesses were found to be infected with the coronavirus. The spread of COVID-19 infection continues unabated even after vaccination has begun. A study done on health-care workers who were vaccinated reported mild symptomatic breakthrough infection. Studies on breakthrough infections, their severity, and outcome have not been widely done in India.
Objectives: This study estimates the COVID-19 test positivity rate among patients reporting to the flu corner of a tertiary care center, their contact history, vaccination status, and the rate of breakthrough infection among the cases.
Methodology: A prospective longitudinal study was done on people who presented to the flu corner of McGANN Teaching District Hospital, Shivamogga, in June 2021. Preliminary data were collected through direct interviews. Later positive cases of COVID-19 were followed up till a documented clinical outcome. Responses were made into a database and descriptive statistics were done.
Results: The test positivity rate of COVID-19 is 25%. Around 16% of the people who tested positive were asymptomatic. One out of four of the participants was vaccinated with at least one dose of the COVID-19 vaccine. Around 15% of the vaccinated people tested positive.
Conclusion: Our study found that the test positivity rate at our tertiary hospital is higher than the district average. A single dose of COVID-19 vaccination does not seem to be protective against contracting COVID-19 infections. These findings need to be verified through studies in different settings.

Keywords: Breakthrough infection, covaxinTM, COVID-19, COVID vaccine, Covishield

How to cite this URL:
Wilson S, Koppad R, Nagendra K, Kumari S, Liana C, Joseph CA. Test positivity rate, contact history, and vaccination status of COVID-19 among patients visiting flu corner (fever clinic) of a tertiary care health center of Karnataka: A prospective longitudinal study. MRIMS J Health Sci [Epub ahead of print] [cited 2023 Oct 4]. Available from: http://www.mrimsjournal.com/preprintarticle.asp?id=362534

  Introduction Top

In December 2019, groups of patients with viral pneumonia-like illness were found to be infected with a novel type of virus, the coronavirus, which was named the SARS-COV-2. Since then, the disease has spread all across the globe and is now a public health emergency.[1]

The total confirmed cases and count of complicated cases including mortality have since then been cumulating. As of June 13, 2021, according to the World Health Organization, there are 175,306,598 confirmed cases of COVID-19, including 3,792,777 deaths.[2] As of June 10, 2021, a total of 2,156,550,767 vaccine doses have been administered. The COVID-19 test positivity rate of the state of Karnataka was 6.02% as of June 12, 2021.[3] Karnataka has administered 16,955,711 doses of vaccine to date.[4] Test positivity rate of Shimoga district was 9.71% on June 13, 2021.[5]

Vaccinations for COVID-19 are now open to all adults in India. However, the spread of COVID-19 infection continues unabated. A study was done on health-care workers of a health facility who were vaccinated and reports mild symptomatic breakthrough infections.[6] Another study reports that COVID infections have occurred in vaccinated participants but were few and their severity was very low.[7]

Studies on breakthrough infections, their severity, and outcome have not been widely done in India. They help us ascertain the protective efficacy of vaccines, identify the glitches in the vaccination program, and promote vaccination campaigns.


  • To estimate the positivity rate of COVID-19 in patients reporting to Flu Corner of McGann Teaching District Hospital, Shimoga
  • To determine the contact history and vaccination status of all the presenting laboratory-confirmed positive cases
  • To estimate the rate of breakthrough infections and their severity.

  Methodology Top

A prospective longitudinal study was conducted on all patients who presented to the flu corner (fever clinic) of a tertiary health care hospital in June 2021, when around 100 COVID tests were being done daily on an average in our center. Considering test positivity rate as P = 9.71% in June 2021 (5), with the help of formula n = 4pq/d2, where P = 9.71%, q is (1-p) =90.3% and d is absolute precision, =5% with z value is 1.96 for confidence level of 95%. Hence, the calculated sample size was 140. Considering 10% as no response, the minimum required sample size was 154. However, we interviewed 234 participants, well over the calculated minimum sample size.

Simple random sampling was employed (we were ready with computer-generated random numbers every day considering average flu corner attendance was 100 patients per day during the peak period of the second wave) and preliminary data were collected through a personal interview at the flu corner Specimen Referal Form ID (SRFID) generation counter and included basic information and details including contact number, medical history, and vaccination history. Criteria for inclusion in the study were that the case presented to the flu corner for a COVID-19 test and participants who did not consent were excluded from the study. In the next 2 days, details on the outcome of the test, whether positive or negative was obtained through telephonic interviews, and was cross-checked with our COVID testing laboratory reports which were sent to flu corner the next day. During a later follow-up after 2 weeks, the type of treatment undergone, severity of the infection, and outcome of the disease were documented through telephonic follow-up. Brief medical history was collected to conclude whether the participant is symptomatic or asymptomatic and vaccination history on the type of vaccine taken and the number of doses administered was also elicited. Cases in home isolation were considered mild infections and those which required hospital admissions were considered moderate-to-severe cases. All the information was collected after taking informed oral consent and ethical clearance was obtained from the institutional ethical committee before starting the study. Permission from the institutional head was also obtained. Data were entered into an Excel spreadsheet and statistical tests such as percentages, proportions, and Chi-square tests were employed with the help of Epi-info software. The level of significance was set at P = 0.05 and it was two-sided. Similarly, biases were identified as lost to follow-up, sampling bias (as it was a hospital-based study), and interviewer bias (it was tried to reduce by collecting information by only one person). Lost to follow-up bias was minimized by keeping frequent contact with the participant and building a rapport, and interviewer bias was minimized by the completion of the entire data collection by a single person. There were no participants lost to follow-up at the end of the study.

  Results Top

The mean age of the study participants was 33.5 years. COVID-19 infection was more in middle age groups and less in below 20 years of age. 61.40% of the affected were males. The proportion of participants who contracted the disease did not differ by gender (P = 0.345, not significant as P > 0.05) [Table 1].
Table 1: Age- and gender-wise distribution of the study participants

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The percentage of positive COVID-19 cases among people, who presented to the flu corner, for the COVID test was 24.36% (COVID-19 Test positivity rate TPR).

Although Rapid Antigen Test (RAT) was offered to only symptomatic and/or people with recent contact history or those who had to undergo emergency admission and treatment for acute conditions, only 13.60% of RAT tests were positive, compared to 20% positive reverse transcriptase–polymerase chain reaction (RT-PCR) tests. Further, we found that false-negative tests on RAT, considering RT-PCR to be a better test, were 15.31% [Table 2].
Table 2: Outcome of COVID-19 rapid antigen test and reverse transcriptase–polymerase chain reaction tests

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32.05% of the people who presented to the flu corner were contacts of laboratory-confirmed cases and, 45.61% of them were positive. 54.39% of the cases had no known contacts. There was a significant relationship between positive contact history and contracting the disease. People who were contacts were more likely to get the disease. X2 (1, n = 234) =6.36, P = 0.012, significant as P < 0.05 [Table 3].
Table 3: Contact history of participants with a known laboratory-confirmed case

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Around 16% of the people who tested positive were asymptomatic. However, people who were symptomatic at the time of presentation were more likely to test positive. X2 (1, n = 234) =18.64, P = 0.000016, significant as P < 0.05 [Table 3].

25.13% of the participants were vaccinated with at least one dose of any government-approved COVID-19 vaccine. The Covishield vaccine was more administered compared to the CovaxinTM vaccine. Double doses vaccinated were almost half in number compared to single dose vaccinated participants [Table 4].
Table 4: COVID-19 vaccination details of the study participants

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Only 14.89% of vaccinated people tested positive (breakthrough infection). However, a Chi-square test of independence showed that there was no significant relationship between getting vaccinated and not contracting the disease. P = 0.091, not significant as P > 0.05. Of the seven people who tested positive even after being vaccinated, only two were fully vaccinated [Table 5].
Table 5: COVID-19 positivity among vaccinated and unvaccinated individuals

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Out of the 57 positive people, 80.70% had only a mild infection, which required home or hostel isolation and 19.30% had a moderate or severe infection, which required admission to a health facility and high-flow oxygen therapy. However, there seems to be no relationship between vaccination and severity of infection postvaccination [Table 6].
Table 6: Severity of infection in vaccinated and unvaccinated COVID-19-positive participants

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96.50% of those infected recovered in around 10–12 days and had no complications, whereas the rest had complications, including one death [Table 7].
Table 7: Outcome of the disease process with respect to vaccination status

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  Discussion Top

From the current study, we calculated the test positivity rate of COVID-19 among people who presented to the flu corner of the tertiary health facility in a month as 24.36% (mean = 25.01%). However, the test positivity rate of the district was only 9.71% as of June 13, 2021.[5] This difference could be because, since it was a tertiary center, people with severe symptoms visited the flu corner, compared to peripheral centers and kiosks, where more asymptomatic contacts or testing on demand would have been done. However, this could also be a pointer to our COVID care facilities acting as hotspots and resulting in super spread to patients and their attenders.

The infection was more in middle age groups and less in <18 years old. Children and adolescents are more protected and remain in isolation at home due to school and college shut down. However, the working class gets exposed to the disease as they have to come out to the public. Similarly, infection was also found to be more among males. However, there is no significant association between gender and contracting the disease. Minor differences would be because women might be less exposed, and more careful regarding following the COVID-appropriate behavior.

Around 63% of people were offered a RAT test. RAT test was reserved for people who presented with symptoms suggestive of COVID-19 infection, close contacts, or who had to undergo immediate medical intervention or hospital admission. Others and also those who were RAT negative were also subjected to the RT-PCR test.

The false-negative results on the RAT test, considering RT-PCR to be accurate, were 15.31%. Infected persons with false-negative RAT results may not be isolated and can infect others. The false-positive antibody results could also be eliminated after five times dilution with normal human serum.[8]

A study from Israel states that for most infections the source was unknown. Only 24% of people had a known contact history.[9] In our study, around 54% of the positive people had no history of contact with a known laboratory-confirmed case. This can be due to a large number of asymptomatic cases, carrier states, and smaller number of people getting tested. It might also be due to the airborne spread of disease. This calls for active case detection, further probing into whether an airborne spread is occurring.

Out of 243 people, only 20.08% had been vaccinated with at least one dose of the vaccine. Karnataka had vaccinated 3,554,331 people (5.18%) with two doses of vaccine and 18,196,699 (26.56%) people with one dose of the vaccine as on June 28, 2021.[10]

The rate of breakthrough infection in our study was 14.89%. According to a recent statement from the Indian Council of Medical Research, only 2–4/10,000 got infected with COVID-19 after vaccinations in India.[11] A study from Israel documents a 2.6% prevalence of breakthrough infection.[12] A similar study from Chicago reports breakthrough infection to be around 3.52%, but of them, 64% were asymptomatic.[13] A study from New Delhi reports symptomatic COVD-19 infections occurred in 16.9% post any dose of vaccine and after the second dose in 13.3%.[6]

In a randomized-controlled trial, COVID-19 vaccines were found to be safe and efficacious in preventing symptomatic, laboratory-confirmed COVID-19. However, according to Centre for Disease Control and Prevention (CDC), a small percentage of fully vaccinated persons will develop symptomatic or asymptomatic infections with SARS-CoV-2.[14]

A cohort study of 417 persons who were vaccinated with two doses of the vaccine reports that two women had a breakthrough infection.[15]

A total of 12.28% of the positive individuals were vaccinated. However, in the seven fully vaccinated positive people (14.89%), only two people (28.57%) developed a moderate-to-severe infection and required hospitalization. However, the Chi-square test and P value were not statistically significant. This could probably be due to lesser vaccine coverage in the study sample.

Around 4 in 5 participants had mild infections. They were either advised home isolation or government-run hostel isolation facilities and recovered in 10 days. A total of 19.30% had a moderate-to-severe infection and had to be put on high-flow oxygen and hospitalized. Contradicting findings from most available studies, our study reports that there is no significant association between vaccination and severity of infection. This is not conclusive as our sample had a lesser number of vaccinated individuals. However, it needs to be investigated and the strength of association, if any, must be well documented.

A total of 96.50% of cases recovered, whereas 3.50% went in for complications, of which 1 (50%) died. The risk of contracting severe COVID-19 infection that necessitates hospital admission and high-flow oxygen or remdesivir therapy or other interventions remains low. However, there are no sources that correctly predict which set of patients will go in for complications and who will get a mild infection.

The limitations of the study

The coverage of vaccination at the time of the study was less, as the vaccination for the common people were started very recently and many were covered with single dose. These findings are not generalizable because it was a hospital-based study and done in only one center. For better results, it has to be carried out as a community-based study or in multiple centers.

  Conclusion Top

In our study, the test positivity rate for COVID-19 at our facility was high. RAT test gave significant false-negative tests. We observed a significant relationship between positive contact history and contracting the disease. One in four participants was vaccinated with at least one dose of the government-approved COVID-19 vaccine. The rate of breakthrough infection was slightly high. Most of the participants who tested positive had a mild infection and required no hospitalization.


The authors acknowledge the help received from the Shimoga Institute of Medical Sciences and McGANN District Teaching Hospital and the Department of Community Medicine, SIMS, Shimoga.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Soares RC, Mattos LR, Raposo LM. Risk factors for hospitalization and mortality due to COVID-19 in Espírito Santo State, Brazil. Am J Trop Med Hyg 2020;103:1184-90.  Back to cited text no. 1
WHO Corona Virus (COVID-19) Dashboard. Available from: https://covid19.who.int. [Last accessed on 2021 Nov 06].  Back to cited text no. 2
COVID Reports. Available from: https://covid19.karnataka.gov.in/covid-reports/report. [Last accessed on 2021 Nov 06].  Back to cited text no. 3
COVID-19 Portal, Government of Karnataka. Available from: https://covid19.karnataka.gov.in/English. [Last accessed on 2021 Nov 06].  Back to cited text no. 4
Ministry of Health and Family Welfare. Available from: https://www.mohfw.gov.in. [Last accessed on 2021 Nov 06].  Back to cited text no. 5
Tyagi K, Ghosh A, Nair D, Dutta K, Singh Bhandari P, Ahmed Ansari I, et al. Breakthrough COVID19 infections after vaccinations in healthcare and other workers in a chronic care medical facility in New Delhi, India. Diabetes Metab Syndr 2021;15:1007-8.  Back to cited text no. 6
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Brosh-Nissimov T, Orenbuch-Harroch E, Chowers M, Elbaz M, Nesher L, Stein M, et al. BNT162b2 vaccine breakthrough: Clinical characteristics of 152 fully vaccinated hospitalized COVID-19 patients in Israel. Clin Microbiol Infect 2021;27:1652-7.  Back to cited text no. 9
Ministry of Health and Family Welfare, Government of India. Available from: https://www.mohfw.gov.in/pdf/Cumulative Covid Vaccination Coverage Report 27th June 2021.pdf. [Last accessed on 2021 Nov 06].  Back to cited text no. 10
Economictimes.Indiatimes.com. Only 2-4 per 10,000 Got Infected After Vaccination; Not Worrisome: Balram Bhargava, DG ICMR. Available from: https://economictimes.indiatimes.com/news/india/only-2-4-per-10000-got-infected-after-vaccination-not-worrisome-balram-bhargava-dg-icmr/videoshow/82181979.cms. [Last accessed on 2021 Nov 06].  Back to cited text no. 11
Bergwerk M, Gonen T, Lustig Y, Amit S, Lipsitch M, Cohen C, et al. Covid-19 breakthrough infections in vaccinated health care workers. N Engl J Med 2021;385:1474-84.  Back to cited text no. 12
Teran RA, Walblay KA, Shane EL, Xydis S, Gretsch S, Gagner A, et al. Postvaccination SARS-CoV-2 infections among skilled nursing facility residents and staff members – Chicago, Illinois, December 2020-March 2021. Am J Transplant 2021;21:2290-7.  Back to cited text no. 13
CDC COVID-19 Vaccine Breakthrough Case Investigations Team. COVID-19 Vaccine breakthrough infections reported to CDC – United States, January 1-April 30, 2021. MMWR Morb Mortal Wkly Rep 2021;70:792-3.  Back to cited text no. 14
Hacisuleyman E, Hale C, Saito Y, Blachere NE, Bergh M, Conlon EG, et al. Vaccine breakthrough infections with SARS-CoV-2 variants. N Engl J Med 2021;384:2212-18.  Back to cited text no. 15

Correspondence Address:
Sijin Wilson,
Vazheparambil House, Kumaranelloor Post, Anayamkunnu, Mukkam, Kozhikode - 673 602, Kerala
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjhs.mjhs_60_22


  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]


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