Introduction

It is already known that Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a novel coronavirus that was first detected in Wuhan, China, 2019 and it was named Coronavirus Disease 2019 (COVID-19) (del Rio & Malani, 2019; WHO, 2020). Actually SARS-CoV-2 is dangerous virus because of its highly contagious nature. Regarding human-to-human transmission it occurs approximately 2 to 10 days before symptom arises and this particular feature makes difference in comparison to other respiratory viruses (WHO, 2020; Sohrabi, et al, 2020 & Guan, et al, 2020). Respiratory secretions are the way of this virus transmission from person to person. Large droplets from coughing, sneezing, or a runny nose land on surfaces within two meters of the infected person. Evidence suggests that SARS-CoV-2 remains viable for at least 24 hours on hard surfaces and up to eight hours on soft surfaces (van Doremalen, et al, 2020). The virus is transferred to another person through hand contact on a contaminated surface then touching the mouth, nose, or eyes. Individuals with COVID-19 can present with influenza like illness and respiratory tract infection demonstrating fever (89%), cough (68%), fatigue (38%), sputum production (34%) and/or shortness of breath (19%) (Guan, et al, 2020). The spectrum of disease severity ranges from an asymptomatic infection, mild upper respiratory tract illness, severe viral pneumonia with respiratory failure and/or death. Current reports estimate that 80% of cases are asymptomatic or mild; 15% of cases are severe (infection requiring oxygen); and 5% are critical requiring ventilation and life support (WHO, 2020).  At present, the mortality rate is 3 to 5%, with new reports of up to 9%, in contrast to influenza, which is around 0.1% (WHO, 2020). The rates of admission to an intensive care unit (ICU) are approximately 5% (Guan, et al, 2020). Half of patients admitted to hospital (42%) will require oxygen therapy (Guan, et al, 2020). Numerous evidences suggest, individuals at highest risk of developing severe COVID-19 disease requiring hospitalization and/or ICU support are those who are older, male, have at least one co-existing co-morbidity (WHO, 2020; Guan, et al, 2020; Chen, et al, 2020; Zhou, et al, 2020 & Xie, et al, 2020). In this situation it is timely study to investigate diagnostic modalities of COVID-19 by Rapid Antigen and RTPCR with clinical features and outcomes.

Methods:

Study design: This was a cross-sectional study.

Study place: Data were collected from Bangabandhu Sheikh Mujib Medical University.

Study period: This study was conducted for a period of 3 months started from Feb to May 2022.

Study population: Study was conducted among patients admitted in Bangabandhu Sheikh Mujib Medical University

Sample size: The sample size for this study was determined by the following equation

 Z²pq

                                               n = -------------

d²

Were,

n = sample size                                 

Z = 1.96 (value of 95% CI)     

p= probability of outcome 50%

q = 1- p

d = standard error (5%)

So total sample was 384 but to increase statistical power total sample was taken 754.

Sampling technique: Non probability convenient sampling method was used to select sample population.

Data collection technique: Data were collected from the respondents through hospital record review. The questionnaire was used after verbal consent of the respondents and their voluntary participation was sought. 

Ethical consideration: Initial ethical clearance was taken from the ethical review committee of the Bangabandhu Sheikh Mujib Medical University.

• Consent was taken from every individual who will the part of the study
• Confidentiality of the person and the information were maintained, observed and unauthorized persons will not access to the data

Results

Age group (yr)	Frequency	Percentage
≤20	130	17.2
21-40	304	40.3
41-60	211	28.0
>60	109	14.5
Mean±SD	39.40±19.03
Total	754	100.0

Table 1. Age group distribution (n=754)

Mean age of the respondents was 39.40±19.03 years. Bulk of the respondents (40.35%) came from 21-40 years age group followed by 28.0% from 41-60 years, 17.2% from ≤20 years and 14.5% from >60 years.

Figure 1. Gender distribution (n=754)

Male and female were 55.80% and 44.20%.

Figure 2. Educational level distribution (n=754)

Illiterate, Primary, SSC, HSC, Graduation and Post-graduation educational level were 6%, 12.60%, 13.30%, 18.30%, 18.80% and 31% respectively.

Figure 3. Occupation distribution (n=754)

About 25.20%, 22.40%, 19.10% and 12.70% engaged in service, household activities, business and study respectively.

Figure 4. Diagnosis of COVID-19 by Rapid Antigen and RTPCR

Among 754 patients 158(21.0%) was COVID-19 positive by Rapid Antigen whereas it was 154(20.40%) by RTPCR.

Age group	COVID-19 test by RTPCR		Total	χ2	p value
	Positive	Negative
	n(%)	n(%)
≤20	17(2.3)	113(15.0)	130(17.2)	14.355	0.002
21-40	81(10.7)	222(29.4)	303(40.2)
41-60	40(5.3)	171(22.7)	211(28.0)
>60	16(2.1)	94(12.5)	110(14.6)
Total	154(20.4)	600(79.6)	754(100.0)
	COVID-19 test by Rapid Antigen
≤20	18(2.4)	112(14.9)	130(17.2)	13.095	0.004
21-40	82(10.9)	221(29.3)	303(40.2)
41-60	41(5.4)	170(22.5)	211(28.0)
>60	17(2.3)	93(12.3)	110(14.6)
Total	158(21.0)	596(79.0)	754(100.0)

Table 2. Association between age group and COVID-19 positive by RTPCR and Rapid Antigen

Statistically significant association was found between age group and COVID-19 positive by RTPCR (p=0.002<0.05) and Rapid Antigen (p=0.004<0.05).

Gender	COVID-19 test by RTPCR		Total	χ2	p value
	Positive	Negative
	n(%)	n(%)
Male	99(13.1)	322(42.7)	421(55.8)	5.604	0.018
Female	55(7.3)	278(36.9)	333(44.2)
Total	154(20.4)	600(79.6)	754(100.0)
	COVID-19 test by Rapid Antigen
Male	101(13.4)	320(42.4)	421(55.8)	5.303	0.024
Female	57(7.6)	276(36.6)	333(44.2)
Total	158(21.0)	596(79.0)	754(100.0)

Table 3. Association between gender and COVID-19 positive by RTPCR and Rapid Antigen

Statistically significant association was found between gender and COVID-19 positive by RTPCR (p=0.018<0.05) and Rapid Antigen (p=0.024<0.05).

Nutritional status	COVID-19 test by RTPCR		Total	χ2	p value
	Positive	Negative
	n(%)	n(%)
Underweight	18(2.4)	45(6.0)	63(8.4)	61.527	0.001
Normal	49(6.5)	385(51.1)	434(57.6)
Overweight	51(6.8)	125(16.6)	176(23.3)
Obese	36(4.8)	45(6.0)	81(10.7)
Total	154(20.4)	600(79.6)	754(100.0)
	COVID-19 test by Rapid Antigen
Underweight	18(2.4)	45(6.0)	63(8.4)	66.321	0.001
Normal	50(6.6)	384(50.9)	434(57.6)
Overweight	52(6.9)	124(16.4)	176(23.3)
Obese	38(5.0)	43(5.7)	81(10.7)
Total	158(21.0)	596(79.0)	754(100.0)

Table 4. Association between nutritional status and COVID-19 positive by RTPCR and Rapid Antigen

Statistically significant association was found between nutritional status and COVID-19 positive by RTPCR (p=0.001<0.05) and Rapid Antigen (p=0.001<0.05).

Clinical Features	Mean±SD (Day)
Fever	6.98±3.26
Cough	6.34±3.33
Respiratory distress	4.55±2.69

Table 5. Clinical Features of COVID-19 by RTPCR

Mean days of suffering of fever, cough and respiratory distress was 6.98±3.26, 6.34±3.33 and 4.55±2.69.

Figure 5. SpO2 level of COVID-19 patients (n=158)

Saturation of Peripheral Oxygen (SpO2) level 91-95% (concerning), 86-90% (low), 80-85% (affects brain) and <80% (cyanosis) were found among 56.30%, 24.70%, 17.10% and 1.90% COVID-19 patients.

Discussion

In December 2019, a novel coronavirus now recognized as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was identified as the cause of a cluster of pneumonia cases in Wuhan, a city in the Hubei Province of China. It rapidly spread, resulting in a global pandemic. In February 2020, the World Health Organization named the disease COVID-19, which stands for coronavirus disease 2019 (WHO, 2020).  The possibility of COVID-19 should be considered in anyone with new-onset fever and/or respiratory symptoms. Although cough and dyspnea are considered the classic respiratory features of COVID-19, other respiratory symptoms such as sore throat, rhinorrhea, and nasal congestion are also commonly reported. As SARS-CoV-2 is prevalent worldwide, clinicians should have a low threshold for suspicion of COVID-19. The threshold for suspicion should be particularly low if the individual resides in or has traveled to locations with high rates of community transmission, has had potential exposure to SARS-CoV-2 in an outbreak setting or as a close contact of someone with confirmed or suspected infection, or resides in a congregate setting. There are no specific clinical features that can reliably distinguish COVID-19 from other viral respiratory infections (Struyf et al, 2020). Nevertheless, some features may warrant a higher level of clinical suspicion (Cohen et al, 2020; Tostmann et al, 2020; Makaronidis et al, 2020). Several studies have suggested that loss of taste or smell are the symptoms most strongly associated with a positive SARS-CoV-2 test (Tostmann et al, 2020; Akinbami et al, 2021; Dawson et al, 2021). Development of dyspnea several days after the onset of initial symptoms is also suggestive of COVID-19 (Cohen et al, 2020). Other, more unusual findings, such as new-onset pernio-like lesions (eg, "COVID toes"), also heighten suspicion for COVID-19. However, none of these findings definitively establish the diagnosis of COVID-19 without microbiologic testing. Considering current trend of COVID-19 transmission it is logical to assess diagnostic modalities of COVID-19 by Rapid Antigen and RTPCR with clinical features and outcomes among patients in Bangabandhu Sheikh Mujib Medical University. Mean age of the respondents was 39.40±19.03 years. About 21.0% was COVID-19 positive by Rapid Antigen whereas it was 20.40% by RTPCR. Statistically significant association was found between age group, gender, nutritional status and COVID-19 positive by RTPCR. Mean days of suffering of fever, cough and respiratory distress was 6.98±3.26, 6.34±3.33 and 4.55±2.69. Saturation of Peripheral Oxygen (SpO2) level 91-95%, 86-90%, 80-85% and <80% were found among 56.30%, 24.70%, 17.10% and 1.90% COVID-19 patients. Reported false-negative rates have ranged from less than 5 to 40 percent, although these estimates are limited, in part because there is no perfect reference standard for comparison (Weissleder, Lee & Pittet, 2020; Long et al, 2020). As an example, in a study of 51 patients who were hospitalized in China with fever or acute respiratory symptoms and ultimately had a positive SARS-CoV-2 RT-PCR test (mainly on throat swabs), 15 patients (29 percent) had a negative initial test and only were diagnosed by serial testing (Fang et al, 2020). In a similar study of 70 patients in Singapore, initial nasopharyngeal testing was negative in 8 patients (11 percent) (Lee et al, 2020). In both studies, rare patients were repeatedly negative and only tested positive after four or more tests. However, lower false-negative rates have also been suggested. In one study of 626 patients who had a repeat nasopharyngeal RT-PCR test within seven days of an initial negative test at two large health centers in the United States, 3.5 percent of the repeat tests were positive (Long et al, 2020). Some studies have suggested that a positive antigen test is more likely than a positive RT-PCR test to indicate that infectious virus could be cultured from specimens (Pekosz et al, 2021; McKay et al, 2021). The current study got similar findings. The present study found that among 754 patients 158(21.0%) was COVID-19 positive by Rapid Antigen whereas it was 154(20.40%) by RTPCR. So rapid antigen test gives quite similar result in comparison to RTPCR test. As an example, among 38 RT-PCR-positive specimens, antigen testing was positive for 27 of 28 specimens that were culture positive but only 2 of 10 specimens that were culture negative (Pekosz et al, 2021). However, infectious virus can still be isolated from antigen-negative specimens, and a negative antigen test cannot be used to indicate that a person is not infectious. In another study, infectious virus was cultured from 11 of 124 clinical specimens (9 percent) that were RT-PCR positive but antigen negative (Prince-Guerra et al, 2021).

Conclusion

It is concluded from the study that among 754 patients 158(21.0%) was COVID-19 positive by Rapid Antigen whereas it was 154(20.40%) by RTPCR. Statistically significant association was found between age group, gender, nutritional status and COVID-19 positive by RTPCR and Rapid Antigen. Mean days of suffering of fever, cough and respiratory distress was 6.98±3.26, 6.34±3.33 and 4.55±2.69. Further large-scale study can be conducted to get more precise result.