Disinfectants, Sanitizers & Practices for Creating Safe Living Environment in

COVID-19 Period

Ankush Gupta

HBCSE (TIFR),

May 30, 2020

Disclaimer

This presentation includes:

• the information based on research literature (and not on first hand experiments by me, unless mentioned).

• results applicable for external use on materials or human skin only, NOT for disease treatment or applications inside human bodies.

• only substances that are being used at household level or public spaces. Substances specifically used in clinical/surgical settings are not discussed here in detail.

HBCSE

Types of Human Coronaviruses (HCoVs)

HBCSE

Seven known types of HCoVs

First human Coronavirus HCoV-B814 (sample not preserved) identified in 1965.

Later, four Coronaviruses were found prevalent in humans

1) HCoV-229E (similar to B814),

2) HCoV-OC43

3) HCoV-NL63

4) HCoV-HKU1

These are responsible for common cold (running nose), and respiratory problems.

New Coronaviruses

5) SARS-CoV (that caused Severe Acute Respiratory Syndrome, or SARS) killed ~800 people in 2003

6) MERS-CoV (that causes Middle East Respiratory Syndrome, or MERS) ~858 deaths since 2012

7) SARS-CoV-2 (the novel coronavirus that causes coronavirus disease 2019, or COVID-19)

• van der Hoek L (2007). Human coronaviruses: what do they cause? Antiviral Therapy 12(4 Pt B):651-8.• https://www.cdc.gov/coronavirus/types.html (accessed May 17, 2020)• https://www.who.int/emergencies/mers-cov/en/ (accessed May 17, 2020)

HBCSE

Structure of SARS CoV-2

3D medical animation still shot showing 2019 novel Coronavirus Structure. Avijit Ranjan, CC BY-SA 4.0https://commons.wikimedia.org/wiki/File:3D_medical_animation_coronavirus_structure.jpg (accessed May 17, 2020)

3 major components: Proteins, Lipid envelop and RNA

HBCSE

Inactivation of Virus means…

…altering its chemical structure so that it cannot infect

Viruses are technically not living organisms (unlike other micro-organisms)

HBCSE

SARS-CoV (the 2003 variant)Inactivated (~5 log or 105 times reduction) by

Heat treatment at >70 °C (30 minutes )

1. M. E.R. Darnell, et al. (2004). Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. Journal of Virological Methods 121(1), 85.

2. A.-M. Pagat, et al. (2007). Evaluation of SARS-Coronavirus Decontamination Procedures. Applied Biosafety, 12(2), 100.

Detection

Limit

Study 1

Study 2

at 25 °C and 37 °C by

Acidic conditions below pH = 3. (1 hour)

Alkaline conditions above pH = 12. (1 hour)

formalin and glutaraldehyde (1-2 days)

UV(λ = 254 nm) exposure (10-15 minutes)

at 4 °C, inactivation not complete with pH = 3 and

formalin/glutaraldehyde

HBCSE

pH ~13.0

pH ~13.5

SARS-CoV (the 2003 variant) Alkaline treatment (at 37 °C)

- at pH = 11, negligible effect in 1 hour

- at pH = 12, 5 log reduction in 1 hour

- at pH = 13, instantaneous 3 log reduction

1. M. E.R. Darnell, et al. (2004). Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. Journal of Virological Methods 121(1), 85.

2. A.-M. Pagat, et al. (2007). Evaluation of SARS-Coronavirus Decontamination Procedures. Applied Biosafety, 12(2), 100.

Study 2

HBCSE

A review of 22 studies on human coronaviruses (before SARS-CoV2) indicated inactivation ( > 3 log

reduction) within 1 minute of contact by

a) 62-71% Ethanol

b) 0.5% Hydrogen Peroxide

c) 0.1% Sodium Hypochlorite

d) 0.23% Povidone Iodine

Other biocidal agents (such as following) were less effective

a) 0.05 - 0.2% Benzalkonium Chloride (conflicting results)

b) 0.02% Chlorhexidine Digluconate

HBCSE

Stability of SARS-CoV 2 (The Novel Coronavirus)

• A.W.H. Chin et al. (2020). Stability of SARS-CoV-2 in different Environmental Conditions. Lancet Microbe (Published Online April 2), https://doi.org/10.1016/S2666-5247(20)30003-3

All trials done 3 times. N.D. = Not done; U = UndetectableA virus titre of 6.0/mL approximately means ~106 virus per mL of inoculum

30 min at 56 °C or 5 min at 70 °C was sufficient for inactivation

HBCSE

Stability of SARS-CoV 2 (The Novel Coronavirus)

• A.W.H. Chin et al. (2020). Stability of SARS-CoV-2 in different Environmental Conditions. Lancet Microbe (Published Online April 2), https://doi.org/10.1016/S2666-5247(20)30003-3

In general, the virus was more stable on smooth surfaces.

HBCSE

Stability of SARS-CoV 2 (The Novel Coronavirus)

1.A.W.H. Chin et al. (2020). Stability of SARS-CoV-2 in different Environmental Conditions. Lancet Microbe (Published Online April 2), https://doi.org/10.1016/S2666-5247(20)30003-3

2.N. van Doremalen et al. (2020). Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of Medicine 382, 1564. https://doi.org/10.1056/NEJMc2004973

Surface Persistence (Study 1)

Persistence (Study 2)

Paper/Tissue paper 1 hour

Copper 4 hours

Cloth 1 day

Wood 1 day

Cardboard 1 day

Glass 2 days

Bank Note 2 days

Plastic 4 days 3 days

Stainless Steel 4 days 3 days

Mask (outside) 7 days

Mask (inside) 4 days

Aerosols 4 hours

HBCSE

Stability of SARS-CoV 2 (The Novel Coronavirus)

• A.W.H. Chin et al. (2020). Stability of SARS-CoV-2 in different Environmental Conditions. Lancet Microbe (Published Online April 2), https://doi.org/10.1016/S2666-5247(20)30003-3

# Only 1 of the 3 trials was +ve. U = Undetectable

HBCSE

But we have now many reasons to study disinfectants…

most importantly because we now need to clean, disinfect, sterilize and at some places, sanitize at large scales.

HBCSE

Decision making for Cleaning/Disinfection/Sanitization Practices requires choosing:

• Formulations: Pure substance or solutions (aqueous/non-aqueous)

• Amount/concentrations

• Frequency of use

• Modes of application

1. Spraying in air

2. Spraying on surfaces

3. Applying and Scrubbing (on surfaces)

4. Soak washing

• Safety protocols for persons (doing the cleaning)

Here we look at important properties of effective substances for SARS-CoV2 to help you make above decisions for your needs.

HBCSE

Health Concerns from Disinfectants’ uses

UCSF Institute for Health & Aging, UC Berkeley Center for Environmental Research and Children's Health, Informed Green Solutions, and California Department of Pesticide Regulation (2013). Green Cleaning, Sanitizing, and Disinfecting: A Toolkit for Early Care and Education, University of California, San Francisco School of Nursing: San Francisco,.

There are risks to COVID patients due to

secondary infections that are resistant to

antibiotics (often picked from hospitals and

highly disinfected spaces).

HBCSE

More Reasons for Care in Using Disinfectants

• Risk to Human health (as discussed before)

• Disinfection not being achieved (even with high concentration/amount)

• Decay/breakdown of cleaning chemicals in handling/storage (losing potency)

• Damage to materials (reaction of chemicals with surfaces)

• Harm to natural environment and ecology (we need many microorganisms including

viruses around us to survive!)

HBCSE

Some Common Cleaning/Disinfecting Chemicals (effective for SARS-CoV2)

HBCSE

Alcohols

• Ethanol and isopropyl alcohol most effective (methanol less effective)

• Optimum concentration 60-90% (pure alcohol ineffective—water is necessary!)

https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/chemical.html (accessed May 23, 2020)

Mode of Action:Denaturing and coagulating

proteins

• Not effective against spores (hence insufficient for wounds and clinical settings)

Precautions:

• Evaporate fast (& minimum 20 seconds contact required), hence not suitable for hot surfaces

• Flammable—hence must be stored in cool, well-ventilated area

• Not to be used near hot appliances (such as ovens and cooking stoves)

• Can damage certain plastics, rubber parts of instruments.

HBCSE

Sodium Hypochloride(Hypo, NaOCl, Bleach)

• Reaction with water

NaOCl + H2O HOCl + NaOH

• Reacts strongly with acids

- produces chlorine and related gas

Problems:

- Unstable, decomposes with time

- Risk to humans & other organisms

- Chlorine resistance develops with regular use over few days (already known in bacteria for decades): thus use after soap/detergent cleaning is advised

H. F. Ridgway And B. H. Olson (1982). Chlorine resistance patterns of bacteria from two drinking water distribution systems, Applied And Environmental Microbiology, 44(4), 972 . https://aem.asm.org/content/aem/44/4/972.full.pdf

Mode of Action:HOCl reacts with proteins, enzymes, DNA, and lipids

inactivating microbes within 0.1 sec

Decomposition conditions Precautions

At pH <11 Don’t mix with acids

Temperatures ~> 25 °C Store at cool place, avoid hot places

Contact with metals Don’t store or dilute with metal containers

Light exposure Store in dark places

Na+ OCl–

Cl—O

H

HBCSE

Hydrogen Peroxide• Used in dentistry, laundry and in many household cleaners and

bleaching agents.

• With higher concentrations, effective against all microbes (yeast, fungus, spores and viruses).

• Decomposes to water and oxygen (Final products safe!).

• Not effective on Biofilms (big source of hospital infections). Hence scrubbing needed.

• Old solutions may have lower strength.

• W.C.C. Cheng et al. (2020) Disinfection of N95 respirators by ionized hydrogen peroxide during pandemic coronavirus disease 2019 (COVID-19) due to SARS-CoV-2. Journal of Hospital Infection, Published Online, April 08, https://doi.org/10.1016/j.jhin.2020.04.003

• Schwartz, A. et al. (2020). Decontamination and Reuse of N95 Respirators with Hydrogen Peroxide Vapor to Address Worldwide Personal Protective Equipment Shortages During the SARS-CoV-2 (COVID-19) Pandemic. Applied Biosafety, 25(2), 67.

• www.realco.be/wp-content/uploads/2014/09/Scientific-article-Biofilm-resistance-to-hydrogen-peroxide.pdf (accessed May 24, 2020)

Mode of Action:Free radicals attack lipids, membranes and nucleic acids; higher concentrations can overtake the cellular defences by enzymes.

O—O

H

H

Decomposition conditions Precautions

Presence of enzymes Store in clean containers

Temperatures ~> 25 °C Store at cool place, avoid hot places

Contact with metals Don’t store or dilute in metal containers

Light exposure Store in dark containers and places

• In vapourized form, can be used to disinfect N-95 masks (which should not be done using alcohol or bleach solution!)

HBCSE

Mode of Action:Iodine reacts with lipids and membrane

compounds in microbes, blocks respiratory chain, and coagulates nuclear material

Povidone-Iodine

• An aqueous solution of Iodine complex with Povidone (a water soluble polymer of vinyl pyrrolidone).

• Slow release of free iodine; hence lower toxicity than Tincture iodine (I2 + KI, dissolved in Ethanol and water).

• Less used because coloured stains may appear.

• Iodine has similar reactions as Chlorine but less mild.

https://en.wikipedia.org/wiki/Povidone-iodine (accessed May 24, 2020)

• Can be used as hand disinfectant (longer persistence on skin, as I2 penetrates deeper).

• Low toxicity, but can cause allergies to some (rare cases).

• Least known cases of resistant bacteria strains (inspite of >150 years of use)

• Active over biofilms as well.

HBCSE

Mode of Action:-OH reacts with membrane proteins creating leaks, further reacts with proteins & nucleic acids. Mechanism not fully understood.

Chloroxylenol (PCMX)

• Component of Dettol antiseptic washes for ~90 years.

• Requires few seconds of applications on skin.

• Active on many bacteria, fungi and viruses but not spores Contradictions in results on efficacy with bacteria and safety.

• Low water solubility and low volatility.

• Stable in light, low heat and humidity.

• G. McDonnell and A. D. Russell (1999) Antiseptics and Disinfectants: Activity, Action, and Resistance. Clin. Microbiol. Rev., 12(1), 147.• U.S. Pharmacopeia, http://www.pharmacopeia.cn/v29240/usp29nf24s0_m16420.html, (accessed May 24, 2020).• J.C. Lear et al. (2000). Isolation and study of chloroxylenoland triclosan-resistant strains of bacteria. J Pharm Pharmacol, 52 (Suppl), 126.• WHO (2009). WHO Guidelines on Hand Hygiene in Health Care. https://www.who.int/gpsc/5may/tools/9789241597906/en/• pubchem.ncbi.nlm.nih.gov/compound/Chloroxylenol#section=Springer-Nature-References, (accessed May 24, 2020).

• Stable vapour in sunlight for > 24 hour and in sewage for > 7 days (US-EPA prohibits its discharge in sewage/water bodies without notification).

• Also used in paints, emulsions, adhesives (thus already prevalent in our urban environments).

• P. Auregenosa and many molds have developed resistance to it.

HBCSE

Mode of Action:Disrupts –vely charged lipids bilayers in microbes (similar mechanism to soap)

Benzalkonium Chloride (BAC/BKC)

• Common in many Lizol products (not in all)

• White solid, water soluble

• Non-volatile

• Quaternary ammonium salts, part of “Cationic Surfactants” category

• Also used in some eye drops, nasal and ear drops (not very healthy, controversy about safety)

• Induces resistance to many antibiotics (not just to itself) via many indirect pathways after few months of regular use

• Toxic to many fishes, small animals; low toxicity to humans

M. Kim et al. (2018). Widely Used Benzalkonium Chloride Disinfectants Can Promote Antibiotic Resistance. Applied and Environmental Microbiology, 84 (17) e01201-18; DOI: 10.1128/AEM.01201-18

HBCSE

Chlorhexidine digluconate• Also a quaternary ammonium salt (cationic

surfactant), water soluble

• Used in Savlon antiseptic products

• Part of mouthwashes and skin washes, not safe for eyes

• Fast and High activity against bacteria and enveloped viruses, not so much against spores, fungi and non-enveloped viruses.

• High residual activity

Mode of Action:Chlorhexidine cation binds to –vely charged lipid walls,

causing leaks and coagulates cytoplasmic proteins

• https://pubchem.ncbi.nlm.nih.gov/compound/29089#section=Information-Sources (accessed May 25, 2020)• WHO(2009) The WHO Guidelines on Hand Hygiene in Health Care, https://www.who.int/gpsc/5may/tools/9789241597906/en/• M. E. Wand, et al. (2016) Mechanisms of Increased Resistance to Chlorhexidine and Cross-resistance to Colistin following Exposure

of Klebsiella pneumoniae Clinical Isolates to Chlorhexidine. Antimicrobial Agents and Chemotherapy, 61 (1) e01162-16;• A. Addetia, et al. (2019). A Novel, Widespread qacA Allele Results in Reduced Chlorhexidine Susceptibility in Staphylococcus

epidermidis. Antimicrobial Agents and Chemotherapy, 63(6). DOI: 10.1128/aac.02607-18.

• Although few, but some studies have found resistance in some pathogens. Higher dose, used in clinical settings addresses those infections

HBCSE

Mode of Action:Dissolve the lipid layers and proteins

forming micelles

Soaps and Detergents

• Anionic surfactants (having long chain fatty acids & sulphonic acids)

• Cleaning agents, with inactivating effect on most bacteria/viruses

• Scrubbing is important during cleaning

• But some microbes may survive in some soap/ detergent environments (these play important role to break them down in water bodies)

• Regular use of antibacterial soaps can be problematic.

Nickerson, K.W. and Aspedon, A. (1992), Detergent‐shock response in enteric bacteria. Molecular Microbiology, 6: 957-961. doi:10.1111/j.1365-2958.1992.tb02161.x

HBCSE

AlkaliesMode of Action:

Saponification of lipids in membranes and hydrolysis of nucleotides by OH‒

NaOH, Na2CO3, CaO, KOH, K2CO3

• Very few bacteria and virus survive above pH = 9 (but some like SARS-CoV do!)

• Used to clean & disinfect highly infected buildings.

• Inactivation by alkalis slow process (~1 hour).

• Residue layers after mopping with an alkaline solution a barrier to many common pathogens (also not slippery like detergent mopped surface)

Precautions

• Solutions react with atmospheric CO2 and pH reduces with time (thus should be stored in closed containers).

• Can be corrosive to metals, but not to stone cement floors.

• Can cause skin allergies.

Following substances cannot give solutions with pH > 12

- Ammonia (NH3) solution, pH ~10-12; if mixed with strong alkali (like NaOH), ammonia is lost as gas

- baking soda (NaHCO3), pH ~8-9

- Borax (Na2B4O7), pH ~9-10

Easy-to-make alkali solutions with pH > 121) Caustic soda (NaOH): 2 g per litre solution; pH

~12-132) Washing soda (Na2CO3): 11 g per Litre; pH ~11-

12; difficult to go above pH = 12. A solution of Na2CO3 (10 g) + NaOH (0.5 g) in 1 L water has pH > 12. Advantage: has buffering properties (slow drop in pH)

3) Water extract of well burnt (grey-whitish) ash of wood (or other dried biomass): 50 g in 1 L water after filtration (For some ash, ~100 g may be required)#1 If the ash is too black (partially burnt) or the extract obtained is strongly colored (indicating heavy metal contamination), then it should not be used.#2 May need higher amounts with hard water.

HBCSE

Heat Treatment

• In warm seasons, surfaces exposed to sunlight can develop temperatures >50 °C.

• Exposure to >56 °C for ~0.5 hour is sufficient to deactivate SARS-CoV2.

• Higher temperatures reduce the deactivation time.

• Steam cleaning and autoclaving for 2-5 min will also be highly effective.

HBCSE

Except for alkaline solutions (with not too many commercial formulations), formulations with other listed disinfectants are commercially available and typical concentrations are being included in various recommendations for COVID-19. Small adjustments may be required based on specifics of products in local markets (concentration, purity, etc.), quality of water used for dilution, and local temperature.

HBCSE

Some notes on Application Practices

HBCSE

Sanitization sprays, Fogging have been very common in last 2 months

Recently, Ministry of Health and Family Welfare, Govt. of India has issued advisory against disinfectants spraying on individuals

www.mohfw.gov.in/pdf/AdvisoryagainstsprayingofdisinfectantonpeopleforCOVID19managementFinal.pdf, (accessed May 15, 2020)

HBCSE

U.S. Department of Health & Human Services has advised against disinfectant fogging even in patient-care areas (accessed May 15, 2020).

HBCSE

WHO Advisory (May 15, 2020)“Organic matter can impede direct contact of a disinfectant to a surface and inactivate the mode of action of several disinfectants.”

In indoor spaces, routine application of disinfectants to environmental surfaces by spraying or fogging (also known as fumigation or misting) is not recommended for COVID-19... If disinfectants are to be applied, this should be done with a cloth or wipe that has been soaked in disinfectant.

Some countries have approved no-touch technologies for applying chemical disinfectants (e.g. vaporized hydrogen peroxide) …, devices using UV irradiation have been designed for health-care settings. However, several factors may affect the efficacy of UV irradiation... These technologies supplement but do not replace the need for manual cleaning procedures.

Spraying or fumigation of outdoor spaces, such as streets or marketplaces, is also not recommended to kill the COVID-19 virus or other pathogens because disinfectant is inactivated by dirt and debris and it is not feasible to manually clean and remove all organic matter from such spaces...

Furthermore, streets and sidewalks are not considered to be reservoirs of infection for COVID-19.

Cleaning and disinfection of environmental surfaces in the context of COVID-19 Interim guidance, 15 May 2020. apps.who.int/iris/rest/bitstreams/1277966/retrieve

HBCSE

Association of Occupational and Environmental Clinics, USAhas declared Sodium hypochlorite as an asthmagen

UCSF Institute for Health & Aging, UC Berkeley Center for Environmental Research and Children's

Health, Informed Green Solutions, and California Department of Pesticide Regulation. Green Cleaning, Sanitizing, and Disinfecting: A Toolkit for Early Care

and Education, University of California, San Francisco School of Nursing:San Francisco, California, 2013.

HBCSE

Summary of Best PracticesGeneral Practices during all times

• Scrubbing of hands (hand washing) and surfaces with cleaning agents necessary for full cleaning

• Cleaning mops/clothes should be well soaked for 10 minutes in soap/detergent solutions before and after cleaning

• Aggressive chemicals such as hypochlorite/peroxide to be used only after soap/detergent cleaning

• Safety gear (gloves, face mask) should be used by cleaners

Extreme infected spaces

• Soap/detergent for general purpose cleaning

• Hypochlorite, iodine, hydrogen peroxide, or other disinfectants for fast disinfection of surfaces after cleaning

• Alcohols based sanitizers, Povidone-Iodine solutions, and soaps for hand sanitization (may need moisturizing cream or oils to address skin dryness)

• Spraying may be done in confined spaces (in absence of patients) using hydrogen peroxide or hypochlorite (if other options not available)

• Steam/hot water treatment for heat stable materials (e.g., metallic/ceramic containers) in use

• Full body protection needed for cleaners

HBCSE

Summary of Best PracticesRegular Cleaning of Spaces (homes/public spaces) during the pandemic

• Soap and detergent for regular cleaning of clothes, hands, and high contact surfaces (such as door handles, water taps, bathrooms, and toilets)

• Alkaline solutions for cleaning & persistent sanitization of surfaces (particularly of floors, cooking and eating areas, and bathrooms). If the water is hard, then small amounts of EDTA can be mixed additionally.

• Cold objects and surfaces should be paid more attention (cold food packets/storage spaces may be cleaned with soap water, hydrogen peroxide or alternatives based on food safety considerations)

• Heat/steam treatment- wherever possible and safe

• Ventilation and exposure to direct sunlight, wherever possible

• Simple water-based cleaning where no infection suspected (occasionally used spaces)

• Use of multiple methods and disinfectants in cycles to prevent antimicrobial resistance: For example, chloroxylenol, chlorhexidine, or benzalkoniumchloride based formulations may be used once per month or per two weeks with above mentioned substances in daily use.

In busy Marketplaces and Mandis during the pandemic

• Shopkeepers/vendors may keep cotton clothes/towels wetted with soap/detergent /alkaline solutions (non-volatile disinfectants) for covering of food stocks (e.g. Vegetable baskets) or for quick wiping of common use surfaces (such as payment counter) to create transmission barriers.

HBCSE

Suggested Alternatives to hypochlorite for Sanitization of Public Service Infrastructure#

# Can be supplementary to protocols suggested in NIUA (2020), COVID 19 and Safe Sanitation Practices for Urban Context resource book of GoI advisories and Practitioners’ resources for Indian Cities*Bubbling ozone through water also produces hydrogen peroxide. Release of ozone in air should be controlled, as high concentrations can effect health of humans and other animals and plants.

Safer Alternatives (regular) With Intermittent usage of

Containers, bins, trolleys for storage/ transport of medical waste

Washing soda, lime powder (solids left in bins also reduce odour)

Hypochlorite or hot water

Vehicles: storage spaces (metal/ plastic surfaces )

Detergents Hypochloride or hot water

Vehicles: sitting areas - Hydrogen peroxide sprays- Cotton sheets/covers, washed regularly with

detergent- Handles (high touch surfaces)- soap

- Covers cleaned with chloroxylenol or chlorhexidinewashes

Toilets Detergents, alkaline substances (followed by citrate wash if water is hard)

Acidic toilet cleaners, hydrogen peroxide,

PPEs, aprons Hydrogen peroxide Detergents, hot water

Sewage Effluents Ozone*/peroxide treatment

HBCSE

Other Preventive Strategies• Keeping spaces well ventilated (minimizing closed & confined spaces)

• Minimize waste production (Single use disposables are easiest pathways of community transmissions! – Not sanitized before disposing)

• Ensuring proper use (not disposal!) of waste produced through-• Repair

• Recycling of materials and chemicals

• Composting of biological waste

• Incineration of infectious waste

• Active steps to nurture healthy ecologies: nurturing diversity of plants, wild animals, birds, insects, fungi, bacteria, and viruses in our surroundings

• Maintaining composting units in nearby spaces

• Creating small wild ecological green spaces in localities

• Using healthy microbial cultures (such as lactobacillus) in whatever environmental practices we can (such as in gardening)

HBCSE

Comments, questions, and corrections can be send to

ankush@hbcse.tifr.res.in

Acknowledgements to HBCSE colleagues for valuable discussions and feedback on the presentation.

Sanitize and Disinfect with Awareness, and Only When Needed!

HBCSE