This study evaluated and compared the practically achieved disinfection efficacy of some locally available disinfectants on surfaces and very heavy microbial waste load. In routine hospital practice, disinfection of surfaces like floors and walls may not be required except where they have been contaminated by infectious materials or agents. Thorough cleaning of these surfaces may be sufficient in noncritical areas, although some studies advocate the use of a disinfectant in floor cleaning.[9
] Although cleaning may remove a large number of bacteria, the microorganisms that have been left behind soon begin to grow and accumulate, and may cross-contaminate the clean areas. It is more important to disinfect the “near patient” hand touch areas that are most implicated in transmission via the contaminated hands of the health care workers.[9
] Therefore, use of disinfectants in critical and high-risk areas like burn units and Intensive Care Units (ICUs) is justified,[9
] where the environment may be heavily contaminated with drug-resistant pathogens like MRSA, Klebsiella pneumoniae
, Acinetobacter species and Pseudomonas aeruginosa
] On many occasions, while investigating outbreaks caused by MRSA, we have noted gross contamination of the articles and the surfaces like medicine trolleys, the patients’ cabinets, railing of the beds, the nurses’ lockers, electric switches and door handles, etc.(unpublished data). In various ICUs and emergency wards, 27.3% of the environmental surfaces showed contamination with Staphylococcus aureus
, and 30% of these were MRSA.[14
] Proper disinfection of the surfaces is also important in operation theaters[15
] and other areas to disinfect blood spillages and other grossly infected surfaces. Many studies have emphasized that routine cleaning, hand washing and barrier nursing alone were not sufficient to control protracted outbreaks of MRSA, but required proper disinfection of the environment.[16
A wide range of disinfectants are available commercially that undergo extensive testing in controlled environments before market release. However, often, the products and procedures as described in the literature may not be able to adequately disinfect or decontaminate items when the surfaces have been contaminated with highly resistant or unusual organisms, or if the bioload of microorganisms is very heavy. The matter may be further complicated by the quality of environmental hygiene because of dust and other organic matter. When choosing a disinfectant for specific hospital use, it may be necessary to know the expected number and the types of organisms likely to be present on the surface. It is critical that the disinfectant be selected based on its ability to be effective against the prevalent pathogenic microorganisms that can be transmitted by direct or indirect contact with the environment.[18
] Therefore, we chose to test the disinfectants on multidrug-resistant isolates that are circulating in our hospital environment. The type of surface to be disinfected and applications for the product must always be considered. An ideal disinfectant should have a broad antimicrobial spectrum, should be nonirritating, less toxic, noncorrosive and inexpensive.[9
As expected, this study showed that all disinfectants were highly effective in killing microbes on the smooth steel surface as compared with the rough surface. The decrease in efficacy of the test disinfectants on rough surface may be attributed to presence of organic matter, protection provided to the organisms and increased adherence.[9
] On both surfaces, different disinfectants showed a variable effect on different microorganisms. Only Bacillocid special and DesNet could achieve a 100% kill for all microorganisms. All others showed a variable kill of different microorganisms except Candida albicans
, on which each disinfectant achieved a 100% kill. Similarly, on smooth surface, all disinfectants could achieve a 100% kill on MRSA. Salmonella typhi
appeared to be the most difficult target organism to be killed; only Bacillocid special and DesNet could achieve a 100% kill of this organism on both surfaces. Hi-gene could also achieve a 100% kill on smooth surfaces. Phenolics and Clea-N-Sept were least effective against Salmonella typhi
NCTC 786, which is a standard stain used in the R.W. phenol coefficient test.[2
] The statistical analysis also supported the overall best efficacy achieved by DesNet and Bacillocid special on both surfaces. Clea-N-Sept could achieve a comparable efficacy on smooth surface.
Although phenolic agents exhibit high toxicity and low biodegradability, they are still in use in developing countries because of their low cost. They are considered a health risk by the EPA and NIOSH,[19
] and cannot be used in neonatal, pediatric ICU or on any infant contact surface. Eye irritation, contact dermatitis/utricaria and depigmentation of the skin have been linked to phenol residue contact.[12
] In this study, phenolics showed poor activity on rough surfaces that represent cracks and grooves on the floors and walls, very commonly seen in developing country health care settings. Therefore, better and safer disinfectants are required to replace them.
Chlorine, although being rapidly active on bacteria, viruses and most fungi,[12
] has some disadvantages,[20
] which include effect of pH on stability, reduced efficacy in the presence of organic matter, unpleasant smell, irritation to skin, eyes and mucous membranes and corrosiveness to metals. Various chlorine preparations are commercially available, including sodium and calcium hypochlorite, sodium dichloroisocyanurate, etc. In the present study, the antimicrobial activity of Clean-N-Sept was in the acceptable range. It could achieve a 100% kill on five and six of the seven target organisms on rough and smooth surfaces, respectively. However, its use on metallic surfaces cannot be recommended.
Aldehyde-containing disinfectant, “Bacillocid special” was found to be a very effective antimicrobial agent on almost all the tested organisms on both types of surfaces. Although widely used for the chemical sterilization of heat-sensitive equipments, there are safety concerns as aldehydes cause irritation to skin, eyes and air ways, allergic asthma and contact exema.[21
] Therefore, their use is now discouraged throughout the world. A popular brand of gluteraldehyde has been withdrawn from sale in the UK[1
] and replaced with ortho-phthalaldehyde.
Two quaternary ammonium compound (QAC)-containing products, DesNet and Hi-gene Germitol, were tested in this study. Newer QACs are active against a wide range of microorganisms including yeasts and moulds, are odorless, colorless, noncorrosive and highly stable compounds over a wide range of pH (3–10.5) and temperature. They are relatively stable in the presence of organic matter, have bacteriostatic residual effect on treated surfaces and cause low irritation and low toxicity.[12
] Our study has shown high antimicrobial activity of one of the third-generation QAC formulations (DesNet), but lesser activity was shown by the other disinfectant (Hi-giene) containing benzalkonium chloride.
In this study, we also wanted to test the disinfectants against heavy microbial waste load, which was simulated by immersing culture plates in disinfectants and monitored by in-use test. The microbiological waste is best treated by autoclaving.[23
] However, it is a common practice for microbiologists/technicians working on the bench to discard many infectious items into jars containing disinfectants. Chemical disinfection is also required for the disinfection of sharps, which are dipped in disinfectant solutions. Under such conditions, disinfection is required in the presence of organic matter, a variable pH and temperature conditions, and should be free of toxic and irritant fumes. The best disinfection activity was shown by Bacillocid special, followed by DesNet and Hi-giene. Clea-N-Sept and phenolics could not tolerate the tested bacterial load even for 1 day.
There are some limitations of this study as we did not test for antimycobacterial and antiviral effect of any of the test disinfectants. It can be concluded from the present study that newer QACs with surfactants and aldehyde formulations can be used as general purpose disinfectants. Both the disinfectants are noncorrosive to rubber and metals. However, for safety reasons, QAC formulations may be preferred over potentially toxic aldehydes.