Drops, Droplets and Disinfectants

An altered business environment

The pest control industry is caught as a mere bystander during the prevailing Covid-19 pandemic in spite of the knowledge it held on drops, droplets, hygiene, sanitation and spray technology. It also happened despite of the fact that this industry has the right of access to all areas where people congregate and gather, including sensitive areas such as hospitals, transportation, offices and care giving homes. The government’s decision to close all types of work premises and stop non-essential services left the industry with no choice but to trim down their own activities. Eventually a possibility for business never realized, but it created an opening for contemplation.

The World Health Organization (WHO, 2020a) had promptly announced in one of its mid-February bulletins that the new coronavirus (Covid-19) is a respiratory virus, and it spreads primarily through droplets generated when an infected person coughs or sneezes, or through droplets of saliva or discharge from the nose or mouth. (WHO,2020). It was also let known that surfaces infected with virus laden droplets are one of the methods of transmitting the disease to unsuspecting individuals. The pest control industry and the practitioners are proficient with science of drop sizes and droplets. Another term for droplets namely “aerosol” is also used in the industry. The word “aerosol” was first used colloid chemistry to describe a suspension, in air, gas, liquid or solid of a particle having a diameter less than 50 microns (Flashinski, 1998). Practitioners in the industry know characteristics of a good aerosol which has the capacity to deliver particles in a range that will remain airborne for a sufficient period of time. Such knowledge is now thought to be an advantage for practitioners, who could mobilize themselves to take on the task of disinfection. 

Drops and droplets 

Information on droplet characteristic come handy in understanding their transmission, as well as spread inside indoor environment. This information is also useful in understanding disinfectants and undertaking disinfection work. The information that Covid-19 spread through droplet generated by cough, sneeze, saliva or even speech allows practitioners target areas and surfaces most vulnerable. It has been well reported that sneezing may produce as many as 40,000 droplets between 0.5–12 microns in diameter (Cole & Cook, 1998; Tang et al., 2006) that may be expelled at speeds up to 100 meter per second (Cole & Cook, 1998), whereas coughing may produce up to 3000 droplet nuclei, about the same number as talking for five minutes (Cole & Cook, 1998F; Tang et al., 2000). 

Droplet are drops generally larger than 5 microns in diameter that fall rapidly to the ground under gravity, and therefore are transmitted only over a limited distance less or equal to 1 meter (Atkinson, 2009). Droplets may also contain a “droplet nuclei”, which refer to core of some droplets less or equal to 5 microns in diameter. The droplet nuclei can however remain suspended in air for significant periods of time, allowing them to be transmitted over distances more than 1 meter. Such droplet nuclei floating in the air may be carried by the movement of air. In indoor condition this air movement can happen from simple daily activities such as result of operating of an air conditioning device, people walking around, or the opening of a door between a room and the adjacent corridor or space. In addition, it has been reported that the air temperature differences across an open doorway also cause air exchange to occur between the two areas, providing a second mechanism to allow air into other areas (Atkinson 2009). In addition, it is proven that the vehicle for airborne respiratory disease transmission is the droplet nuclei, which are the dried-out residual of droplets possibly containing infectious pathogens (Wells, 1955). Each of these complex interrelated factors makes tracking movement of droplet and droplet nuclei complex, but important components to understand disinfection work. 

The chemistry of natural droplets produced by humans may be varied. It consists mostly of water, with various inclusions, depending on how it is generated. Such droplets naturally produced from humans, e.g. droplets produced by breathing, talking, sneezing, coughing include various cells types such as epithelial cells and cells of the immune system, physiological electrolytes contained in mucous and saliva e.g. Na⁺, K⁺, Cl^-, as well as, potentially, various infectious agents such as bacteria, fungi and viruses (Atkinson, 2009).

It has been shown that SARS-CoV-2 (Covid-19) remained active on plastic and stainless-steel surfaces for two to three days under the conditions in this experiment. It remained infectious for up to 24 hours on cardboard and four hours on copper. The virus was detectable in aerosols for up to three hours. These times will vary under real-world conditions, depending on factors including temperature, humidity, ventilation, and the amount of virus deposited (NIH, 2020). Without effective surface cleaning, this can represent an important risk for surface-mediated transmission. 

An interesting piece of research was done to show how surface mediated transmission is significant in containment of respiratory disease like Covid-19.  Using a DNA oligonucleotide from cauliflower mosaic virus as a sample in place of SARS-CoV-2 applied on a bed rail, the researchers showed that within 10 hours, the sample DNA had moved from the place of first application and transferred to 41% of all surfaces sampled within the entire ward, with a peak at 52% on Day 3 (Rawlinson, et al 2020). The results from this study show the importance of surface-mediated transmission, particularly in light of the current pandemic.

To limit the transmission of the airborne droplets masks and social distancing is made paramount by health authorities to control Covid 19. Also, disinfectants use was mandated knowing solid surfaces can be contaminated by the virus laden droplets unknowingly left by infected people. In fact, experts in union agree that careful cleaning and disinfection of environmental surfaces are essential elements of effective infection prevention programs. 

Disinfectants and disinfection work

Disinfectants

A list of common disinfectants is presented in Table 1. Each disinfectant has its own characteristics and may and may not work in a given situation. It is thus essential that the label is correctly read and understood before use. However, the most important requirement for all disinfectant to be efficient, is giving the chemical the right contact time. For example, all users of EPA-registered products have been advised in the product label to abide by the specific concentration and contact times listed in order for the disinfectant to achieve an effective reduction in pathogen population. It is evident that some disinfectants need a full 10 min of surface contact time for the product to be effective (West, 2018). 

Table 1: List of commonly used disinfectant

Center for disease control and prevention lists out the following properties of an ideal disinfectant (CDC, 2020):

- Broad spectrum: should have a wide antimicrobial spectrum

- Fast acting: should produce a rapid kill

- Not affected by environmental factors: should be active in the presence of organic matter (e.g., blood, sputum, feces) and compatible with soaps, detergents, and other chemicals encountered in use

- Nontoxic: should not be harmful to the user or patient

- Surface compatibility: should not corrode instruments and metallic surfaces and should not cause the deterioration of cloth, rubber, plastics, and other materials

- Residual effect on treated surfaces: should leave an antimicrobial film on the treated surface

- Easy to use with clear label directions

- Odorless: should have a pleasant odor or no odor to facilitate its routine use

- Economical: should not be prohibitively high in cost

- Solubility: should be soluble in water

- Stability: should be stable in concentrate and use-dilution

- Cleaner: should have good cleaning properties

- Environmentally friendly: should not damage the environment on disposal

Application Method

In spite of choosing the right type of disinfectant what remains the most challenging aspect of disinfection work is its incorrect use. It has been proven that inappropriate over-dilution of disinfectant solutions by applicator or by malfunctioning automated dilution systems may result in applying disinfectants using inappropriately low concentrations affecting the overall efficacy of the work (Boyce, 2016). This is an important measure which need to be taken into consideration in all disinfection work.

Disinfection using manual methods

The method of application of disinfectant is also an important factor in overall efficacy of disinfection work. Studies have found that traditional manual cleaning and disinfection practices in hospitals are often suboptimal (Boyce, 2016). This is often due to a variety of personnel issues that many Environmental Services departments encounter. Failure to follow manufacturer’s recommendations for disinfectant use and lack of antimicrobial activity of some disinfectants against healthcare-associated pathogens also affect the efficacy of disinfection practices.

Multiple studies have shown that manual cleaning and disinfection of surfaces in hospitals remain below optimal level. In many facilities, only 40 to 50 % of surfaces that should be cleaned are wiped by housekeepers (Carling, 2010). In addition, observational methods combined with use of adenosine triphosphate (ATP) bioluminescence have shown that individual housekeeper performance varies considerably. One study found variations among housekeepers in the amount of time spent cleaning surfaces, the number of wipes used in each room, and the level of cleanliness achieved (Boyce, 2010).

The nature of material used have been found in some studies to contribute to the efficacy of the disinfection work. This study showed bacteria were removed more effectively by antibacterial wipes than by microfiber (Ali, 2012). Some disinfectants may even bind to cloths made of cotton or wipes containing substantial amounts of cellulose may reduce the antimicrobial efficacy of the disinfectant (Boyce, 2016). Another study reported that detergent wipes have variable ability to remove pathogens from surfaces, and may in fact transfer pathogens between surfaces (Ramm, 2015). Failure of housekeepers to use an adequate number of wipes per room can result in poor cleaning of surfaces (Boyce, 2010).

Disinfection using spray equipment

Apart from wipes and mops disinfectants are also applied using sprayers to cover large areas which would need a quicker application time. A number of reports are available showing efficacy of sprayers in controlling germs of various nature. Spraying curtains with a disinfectant could provide an effective and efficient means to disinfect privacy curtains (Lloyd, 2014). A combination of directly and indirectly applied thermal fog with exposure time of 10 minute was found effective method for control of virus on outdoor equipment (FAO, 2020). most cleaning and disinfection efforts have focused on hard surfaces, there is increasing evidence that contamination of soft surfaces is also common in health care facilities An improved hydrogen peroxide cleaner disinfectant was effective for decontamination of soft surfaces when applied as a spray with no mechanical wiping (Cadnum, 2015).

However, World Health Organization (WHO) has issued an interim guidance with regard to spraying of disinfectant against Covid-19. This guideline state that in indoor spaces, routine application of disinfectants to environmental surfaces by spraying or fogging (also known as fumigation or misting) is shown to be ineffective and not recommended. Similarly spraying or fogging of outdoor spaces, such as streets or marketplaces, is also not recommended to kill the COVID-19 virus or other pathogens in general. The reason being disinfectant is inactivated by dirt and debris (WHO, 2020b). 

Conclusion

Disinfection services is much more intricate than it is perceived. Practitioners should be aware of each of many steps involved in the work before venturing out to undertake a work. The difficulty comes from the fact that germs are diverse and each one requires a specific method of treatment. The fact is further made complex by choice of disinfectant, the method of application and contact time, each playing a significant role in effectively eliminating the pathogen. 

Lack of auditing skills and tools to evaluate a disinfection task further make the field challenging. It is expected that work in this direction will soon begin and interest to set up expert training is not far in future. Pest control practitioners who are keen to venture into this field need to train themselves and have specialists such as microbiologists, sanitation and hygiene experts in their organization to correctly conduct their work.  The future with droplets and disinfectants is very much open but will need careful evaluation. 

This article was previously published in FAOPMA newsletter July 2020.

Reference

Ali S, et al (2012). J Hosp Infect. 80:192–8. doi: 10.1016/j.jhin.2011.12.005. 

Atkinson J, Chartier Y, Pessoa-Silva CL, et al. Natural Ventilation for Infection Control in Health-Care Settings. Geneva: World Health Organization; 2009.

Boyce JM, et al (2010) Infect Control Hosp Epidemiol. 2010; 31:99–101. doi: 10.1086/649225. 

Boyce JM, et al (2016) J. Infect Control Hosp Epidemiol. 37:340–2. doi: 10.1017/ice.2015.299. 

Boyce, 2016. https://aricjournal.biomedcentral.com/articles/10.1186/s13756-016-0111-x

Cadnum, J.L (2015) https://www.sciencedirect.com/science/article/pii/S0196655315007671

Carling PC, Bartley JM. (2010) Am J Infect Control. 2010;38: S41–50. doi: 10.1016/j.ajic.2010.03.004. 

Cole EC, Cook CE. Characterization of infectious aerosols in health care facilities: an aid to effective engineering controls and preventive strategies. American Journal of Infection Control. 1998;26(4):453–464.

FAO (2020) http://www.fao.org/docs/eims/upload/259687/ak110e00.pdf

Flashinski, 1998 Aerosol formulation. In Pesticide formulations. UNIDO publication.

Llyod, A. et al   (2014).  

https://www.researchgate.net/publication/267907357_Effectiveness_of_a_Sporicidal_Disinfectant_Spray_for_Disinfection_of_Hospital_Privacy_Curtains

NIH, 2020. https://www.nih.gov/news-events/nih-research-matters/study-suggests-new-coronavirus-may-remain-surfaces-days

Ramm L, et al (2015) Am J Infect Control; 43:724–8. doi: 10.1016/j.ajic.2015.03.024. 

Rawlinson, S. et al (2020) Covid-19 pandemic – Let’s not forget surfaces, Journal of Hospital Infection. 05, 022.

Tang JW, et al. Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises. Journal of Hospital Infection. 2006;64(2):100–114.

Wells WF (1955). Airborne contagion and air hygiene. Cambridge, MA: Harvard University Press.

West, A. M (2018) https://aricjournal.biomedcentral.com/articles/10.1186/s13756-018-0340-2

WHO (2020)a https://www.who.int/health-topics/coronavirus#tab=tab_1

WHO (2020)b Cleaning and disinfecting of environmental surfaces in the context of Covid-19. Interim Guidance May 2020.