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Questioning The Etiology Of Plantar Warts During The COVID-19 Pandemic

It is now 11 months since my region of the country shut down in response to the COVID-19 pandemic. There are so many things that have changed significantly in our day-to-day life. My daughter hasn’t set foot inside of her school while my son is COVID-19 tested twice a week so that he can attend his school, which has very small class size cohort. My husband only leaves the house at the times blocked out from his virtual meetings to take my son to and from school, aside from his once-a-week food shopping trip. Their situations are typical of most of the patients I see in my office every day.  

While I have continued to see patients throughout the pandemic, the pace of the day has shifted as have the issues/chief complaints of my patients. I have seen far more stress fractures and extensor tendonitis, which I attribute to people spending their days working shoeless from home and changing their exercise regimens. The cases of infected ingrown toenails are more often linked to attempted “home surgery” and far less so from a pedicure gone wrong. 

One thing that I believe has not changed is the prevalence of patients with plantar warts. During the first six weeks of the pandemic, I did not see patients with verrucae much as we only saw urgent cases in person. When we resumed office visits for all patient issues, patients presenting with warts did not stand out as anything notable. But now, almost a year since people have walked barefoot in any shared environment outside of their own homes, the question is consistent: 

Why do patients continue to contract this surface-spread virus to the bottom of the foot when they haven’t been in high-transmission locations or perhaps even outside the home during this time?   

Verrucae plantaris, or plantar warts, are caused by the human papillomavirus (HPV) infecting keratinocytes of the plantar aspect of the foot.1 Once the wart is present, HPV sheds by way of desquamated epithelial cells and these viral particles can then infect other sites and hosts. Contact with viral particles occurs directly to a plantar wart or indirectly with surfaces such as floors, socks, shoes and sports equipment.2 Preceding microtrauma can facilitate entry to the epidermal barrier of the plantar skin by the virus. Once HPV finds its way to this layer of the basal epithelium, the virus binds with cellular receptors. The now infected cell can have an incubation period of one to 20 months before the viral DNA establishes itself within a host cell.3

The most likely ways to develop a plantar wart are to have a preexisting wart or have close contact with someone who has a wart. The high viral load associated with the lesion leads to increased viral shedding and spread to adjacent body surface and ground surfaces. Walking barefoot where others have walked is a risk, which is increased in areas of rough surfaces that promote microtrauma and moist places, such as communal showers and locker rooms.1 While researchers have documented a higher risk of verruca with use of shower rooms in comparison to those who only used the locker room, having family members in the same household with warts and being in the same school classroom as others with warts showed even higher prevalence for development of warts than swimming pools and communal shower use.4-6

Human papillomavirus can survive on surfaces for months to years.1 Some assume that bleach will deactivate HPV but I had a difficult time finding any specific study demonstrating this to be true. While I did not come across studies looking at the effectiveness of disinfectants to surfaces against HPV, there are many studies of transvaginal ultrasound probes showing continued HPV contamination even with proper hospital disinfectant use. High-level disinfectant glutaraldehydes have no effect on HPV while high concentration hydrogen peroxide is effective.7 Hypochlorite is effective in deactivating HPV and was a control in studies looking at other means since it is not compatible with the materials used in some medical devices. Using hypochlorite as the positive control, researchers found that Ultraviolet C (UVC) radiation and sonicated hydrogen peroxide are virucidal against HPV.7,8  

Ortho-phthalaldehyde appeared to be ineffective in many trials but a more recent August 2020 study in the American Journal of Infection Control determined that the level of infectious virions from HPV-induced lesions falls below those in the assays studied and that ortho-phthalaldehyde is likely to be effective with a proper disinfection process.7,9 In my mind, none of this leads to a good answer on what people should use to rid household fomites of viral particles.

In Conclusion

Reviewing all of this leads back to a reality that my patients are not happy to accept. First, that incubation periods can be very long, making the true source of infection hard to pinpoint. Second, the source of plantar wart infection is likely their own home. Third, there is currently no available evidence to show which common home disinfectants will adequately kill HPV.7 

Their kids have not shared a classroom with a large number of other kids nor are communal showers and locker rooms widely open during the past 11 months. Travel is infrequent at most so hotel rooms and hotel bathrooms are not likely sources either. 

My advice to not be barefoot at home rings true as a best defense against the infection of plantar warts as it does for the many musculoskeletal issues that I have seen in increased number in my office through the pandemic. Unfortunately, this conclusion continues to disappoint them all.

Dr. Schwartz is the Scientific Conference Chair and a Past President of the American Association for Women Podiatrists. She is board-certified in foot surgery by the American Board of Foot and Ankle Surgery and is in private practice with Foot and Ankle Specialists of the Mid-Atlantic in Washington, DC and Chevy Chase, MD.

References

1.  Witchey DJ, Witchey NB, Roth-Kauffman MK, Kauffman MM. Plantar warts: epidemiology, pathophysiology, and clinical management. J Am Osteopath Assoc. 2018;118(2):92-105.  

2. Sanclemente G, Gill DK. Human papillomavirus molecular biology and pathogenesis.  J Eur Acad Dermatol Venereol.  2002;220(3):231-240.

3. Longworth MS, Laimins LA. Pathogenesis of human papillovavirus in differentiating epithelia. Microbiol Mol Biol Rev. 2004;68(2):362-372.

4.  Johnson LW. Communal showers and the risk of plantar warts. J Fam Pract. 1995;40(2):136-138.

5. Bruggink SC, Eekhof JAH, Egbers PF, van Blijswijk SCE, Assendelft WJJ, Gussekloo J. Warts transmitted in families and schools: a prospective cohort. Pediatrics. 2013;131(5):928-934.

6. van Haalen FM, Bruggink SC, Gussekloo J, Assendelft WJJ, Eekhof JAH. Warts in primary schoolchildren: prevalence and relation with environmental factors. Br J Dermatol. 2009;161(1):148-152.

7. Meyers C, Millci J, Robison R. UVC radiation as an effective disinfectant method to inactivate human papillomaviruses. PLoS One. 2017;12(10):e0187377. 

8. Ryndock E, Robison R, Meyes C. Susceptibility of HPV16 and 18 to high level disinfectants indicated for semi-critical ultrasound probes. J Med Virol. 2016;88(6):1076-1080.

9. Ozvun MA, Bondu V, Patterson NA, Bennet EC, McKee RG, Wazman AG.  Assessing the efficacy of human papillomavirus disinfection and the risk of transmission from clinical lesions. Am J Infect Control. 2020;48(8):53-54.

10. Solovey M. Popular disinfectants do not kill HPV. Science Daily. Available at: https://www.sciencedaily.com/releases/2014/02/140212132944.htm  . Published February 12, 2014. Accessed February 1, 2021. 

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