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Charles N Haas

Publications and source records attributed to Charles N Haas.

7 recordsLinked to original sources
PubMed2003

Effect of initial microbial density on inactivation of Giardia muris by ozone.

Inactivation of microorganisms by disinfectants frequently shows non-linear behavior on a semilogarithmic plot of log survival ratio versus time. A number of models have been developed to depict these deviations from Chick's Law. Some of the models predict that the log survival ratio (at a particular disinfectant dose and contact time, even in absence of demand) would be a function of the initial concentration of microorganisms (N(0)), while other models do not predict such an effect. The effect of N(0) on the survival ratio has not been deliberately tested. This work examined the inactivation of Giardia muris by ozone in batch systems, deliberately varying the disinfectant dose and N(0). It was found that the models predicting a dependency of survival on N(0) gave a better description to the data than models that did not predict such a dependency. Hence there is an apparent decrease in disinfection efficiency of ozone against Giardia muris (at pH 8 and 15 degrees C) as the initial microorganism concentration decreases. This phenomena should be taken into account by both disinfection researchers and by process design engineers.

Animals↗
PubMed2003

Inactivation of feline calicivirus and adenovirus type 40 by UV radiation.

Little information regarding the effectiveness of UV radiation on the inactivation of caliciviruses and enteric adenoviruses is available. Analysis of human calicivirus resistance to disinfectants is hampered by the lack of animal or cell culture methods that can determine the viruses' infectivity. The inactivation kinetics of enteric adenovirus type 40 (AD40), coliphage MS-2, and feline calicivirus (FCV), closely related to the human caliciviruses based on nucleic acid organization and capsid architecture, were determined after exposure to low-pressure UV radiation in buffered demand-free (BDF) water at room temperature. In addition, UV disinfection experiments were also carried out in treated groundwater with FCV and AD40. AD40 was more resistant than either FCV or coliphage MS-2 in both BDF water and groundwater. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in BDF water were 109, 55, and 16 mJ/cm(2), respectively. The doses of UV required to achieve 99% inactivation of AD40, coliphage MS-2, and FCV in groundwater were slightly lower than those in BDF water. FCV was inactivated by 99% by 13 mJ/cm(2) in treated groundwater. A dose of 103 mJ/cm(2) was required for 99% inactivation of AD40 in treated groundwater. The results of this study indicate that if FCV is an adequate surrogate for human caliciviruses, then their inactivation by UV radiation is similar to those of other single-stranded RNA enteric viruses, such as poliovirus. In addition, AD40 appears to be more resistant to UV disinfection than previously reported.

Adenoviruses, Human↗
PubMed2003

Chlorine inactivation of adenovirus type 40 and feline calicivirus.

Ct values, the concentration of free chlorine multiplied by time of contact with virus, were determined for free-chlorine inactivation experiments carried out with chloroform-extracted (dispersed) and non-chloroform-extracted (aggregated) feline calicivirus (FCV), adenovirus type 40 (AD40), and polio virus type 1 (PV-1). Experiments were carried out with high and low pH and temperature conditions. Ct values were calculated directly from bench-scale free-chlorine inactivation experiments and from application of the efficiency factor Hom model. For each experimental condition, Ct values were higher at pH 8 than at pH 6, higher at 5 degrees C than at 15 degrees C, and higher for dispersed AD40 (dAD40) than for dispersed FCV (dFCV). dFCV and dAD40 were more sensitive to free chlorine than dispersed PV-1 (dPV-1). Cts for 2 log inactivation of aggregated FCV (aFCV) and aggregated PV-1 (aPV-1) were 31.0 and 2.8 orders of magnitude higher than those calculated from experiments carried out with dispersed virus. Cts for 2 log inactivation of dFCV and dAD40 in treated groundwater at 15 degrees C were 1.2 and 13.7 times greater than in buffered-demand-free (BDF) water experiments at 5 degrees C. Ct values listed in the U.S. Environmental Protection Agency (EPA) Guidance Manual were close to, or lower than, Ct values generated for experiments conducted with dispersed and aggregated viruses suspended in BDF water and for dispersed viruses suspended in treated groundwater. Since the state of viruses in water is most likely to be aggregated and associated with organic or inorganic matter, reevaluation of the EPA Guidance Manual Ct values is necessary, since they would not be useful for ensuring inactivation of viruses in these states. Under the tested conditions, dAD40, dFCV, aFCV, dPV-1, and aPV-1 particles would be inactivated by commonly used free chlorine concentrations (1 mg/liter) and contact times (60 to 237 min) applied for drinking water treatment in the United States.

Adenoviruses, Human↗
PubMed2002

On the risk of mortality to primates exposed to anthrax spores.

Current events have heightened the importance of understanding the risks from inhalation exposure to small numbers of spores of Bacillus anthracis. Previously reported data sets have not been fully assessed using current understanding of microbial dose response. This article presents an assessment of the reported primate dose-response data. At low doses, the risk to large populations of low doses of inhaled spores (e.g., < 100) is not insignificant.

Administration, Inhalation↗
PubMed2002

The role of risk analysis in understanding bioterrorism.

Recent events have made the domestic risk from bioterrorism more tangible. The risk management process so far, however, has not benefited from many of the contributions that analysts, communicators, and managers can make to the public discourse. Risk professionals can contribute much to the understanding of and solutions to bioterrorist events and threats. This article will provide an overview of the bioterrorism problem and outline a number of areas to which members of the Society for Risk Analysis, and other risk practitioners, could usefully contribute.

Anthrax↗
PubMedDate not supplied

Comparison of tissue culture and animal models for assessment of Cryptospridium parvum infection.

The current increased interest for using tissue culture as a surrogate for mouse infection to assess Cryptospridium viability suggests that a comparison of the two models is essential for data interpretation. Therefore, a need remains for a statistical comparison that can demonstrate if infection and inactivation predicted by new tissue culture models are comparable with those predicted by animal models. Data from a total of 31 dose-response trials using both tissue culture and mouse models to assess C. parvum infectivity were compared. The dose needed to infect 50% of the tissue cultures (ID(50)) was also compared to each ID(50) in mice. Average ID(50)s developed using the logit dose-response method for tissue culture and mice were 8 and 107, respectively, suggesting that tissue culture was more sensitive to infection. However, correlation (r) between tissue culture and mouse infectivity was statistically significant (0.9167 [95% CI=0.8428 to 0.9594, p<0.0001]). Comparison of oocyst disinfection by UV and chlorine dioxide showed no significant difference between inactivation predicted by tissue culture and mouse models (p=0.8893; t=0.0141; n=21). These results demonstrate that tissue culture can successfully be used to measure C. parvum infection and can be used for determining inactivation in disinfection studies.

Adenocarcinoma↗