The chain of infection involves six inter-linked components: the infectious agent, a reservoir, portal of exit, mode of transmission, portal of entry and a host. This is the sequence by way of which transmission occurs to a susceptible host. Breaking the chain at any one point or more can prevent the spread of infection.

All respiratory viruses including SARS-CoV-2 share a common portal of entry, the respiratory tract. They are inhaled. This is the main mode of transmission, which occurs through droplets and aerosols produced during coughing, sneezing, or just talking, singing, or breathing or direct contact with contaminated surfaces or objects (fomites) in the patient’s environment. The virus may also enter the body through the mouth.

The throat mucosa is an important “epicenter” of viral replication, which is common to many upper respiratory viruses.¹, including Covid-19, which can also present as a mild illness of the upper respiratory tract. Evidence has shown active virus replication in tissues of the upper respiratory tract leading to high viral shedding in the early stage of the infection when the infection is still mild. The peak levels were reached before the fifth day and were more than 1000 times higher than with SARS, which makes Covid-19 a much more infectious and easily transmissible disease as it does not have to travel to the lungs to replicate.^2-4 URIs are also most contagious during the first 2 or 3 days after the onset of symptoms. The viral load profile of SARS-CoV-2 is similar to that of influenza, which is highest at around the time of symptom onset.⁵ 

Because of the throat tropism of the respiratory viruses, gargling with antiseptic formulation such as povidone-iodine (PVP-I) may be a potentially useful strategy in controlling the spread of the URIs as well as Covid-19. Reducing the amount of virus at the initial stage of infection might positively influence the course of the disease. ⁶ 

PVP-I is an extensively used antiseptic with the broadest spectrum of antimicrobial activity compared to other available antiseptics. Rapid onset of action, more persistent effect, lack of reported bacterial resistance and an excellent safety profile are the other striking features of PVP-I. ^7,8 PVP-I gargle has been found to inactivate several respiratory viruses including adenovirus, mumps, rhinovirus, measles and influenza.^9,10  In vitro studies have shown significant virucidal activity of PVP-I against Sudden Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS) coronaviruses as well as SARS-CoV-2. ¹¹ The virucidal activity is evident as early as 15 seconds. ⁶ 

“Prevention is always better than cure”…Preventive measures to break the chain of transmission at an early stage of the disease have an important role in controlling the spread of infections, particularly from asymptomatic or presymptomatic carriers of the infection. This can be done by interventions such as handwashing, cough hygiene, physical distancing, wearing a face mask and being updated with vaccination. To this can be added gargling, a simple and economical strategy, which will help to break the chain of transmission at the portal of entry. 

References 

1. Panta P, et al. Do saline water gargling and nasal irrigation confer protection against COVID-19? Explore (NY). 2021;17(2):127-9.
2. Wölfel R, et al. Virological assessment of hospitalized patients with COVID-2019. Nature. 2020;581(7809):465-9. 
3. O’Donnell VB, et al. Potential role of oral rinses targeting the viral lipid envelope in SARS-CoV-2 infection. Function. 2020;1(1):zqaa002.
4. Charité - Universitätsmedizin Berlin. "Coronavirus: Virological findings from patients treated in a Munich hospital." Science Daily, 3 April 2020. 
5. To KK, et al. Temporal profiles of viral load in posterior oropharyngeal saliva samples and serum antibody responses during infection by SARS-CoV-2: an observational cohort study. Lancet Infect Dis. 2020;20:565–574.
6. Tsai C, et al. Possible beneficial role of throat gargling in the coronavirus disease pandemic. Public Health. 2020;185:45-6. 
7. Lachapelle JM, et al. Antiseptics in the era of bacterial resistance: a focus on povidone iodine. Clin Pract. 2013;10:579–92. 
8. Eggers M. Infectious disease management and control with Povidone Iodine. Infect Dis Ther. 2019;8(4):581-93. 
9. Kanagalingam J, et al. Practical use of povidone-iodine antiseptic in the maintenance of oral health and in the prevention and treatment of common oropharyngeal infections. Int J Clin Pract. 2015;69(11):1247-56. 
10. Vergara-Buenaventura A, et al. Use of mouthwashes against COVID-19 in dentistry. Br J Oral Maxillofac Surg. 2020;58(8):924-7. 
11. Anderson DE, et al. Povidone-iodine demonstrates rapid in vitro virucidal activity against SARS-CoV-2, the virus causing COVID-19 disease. Infect Dis Ther. 2020:9(3):669-75.