Health risks of enteric viral infections in children.

Children are at a greater risk of infections from serious enteric viral illness than adults for a number of reasons. Most important is the immune system, which is needed to control the infection processes. This difference can lead to more serious infections than in adults, who have fully developed immune systems. There are a number of significant physiological and behavioral differences between adults and children that place children at a greater risk of exposure and a greater risk of serious infection from enteric viruses. Although most enteric viruses cause mild or asymptomatic infections, they can cause a wide range of serious and life-threatening illnesses in children. The peak incidence of most enteric viral illnesses is in children <2yr of age, although all age groups of children are affected. Most of these infections are more serious and result in higher mortality in children than adults. The fetus is also affected by enterovirus and infectious hepatitis resulting in significant risk of fetal death or serious illness. In addition to the poliovirus vaccine, the only vaccine available is for hepatitis A virus (HAV). A vaccine for rotavirus has currently been withdrawn, pending review because of potential adverse effects in infants. No specific treatment is available for the other enteric viruses. Enteric viral infections are very common in childhood. Most children are infected with rotavirus during the first 2yr of life. The incidence of enteroviruses and the viral enteric viruses ranges from 10% to 40% in children and is largely dependent on age. On average, half or more of the infections are asymptomatic. The incidence of hepatitis A virus is much lower than the enteric diarrheal viruses. There is no current evidence for hepatitis E virus (HEV) acquisition in children in the U.S. Enteric viral diseases have a major impact on direct and indirect health care costs (i.e., lost wages) and amount to several billion dollars a year in the U.S. Total direct and indirect costs for nonhospitalized cases may run from $88/case for Norwalk virus to $1,193/case for enterovirus aseptic meningitis. Direct costs of hospitalization ran from $887/case for Norwalk virus to $86,899/case for hepatitis A. These costs are based on 1997-1999 data. Generally, attack rates during drinking water outbreaks are greater for children than adults. The exception appears to be hepatitis E virus where young adults are more affected. However, pregnant women suffer a high mortality, resulting in concurrent fetal death. Also, secondary attack rates are much higher among children, probably because of fewer sanitary habits among this age group. Overall, waterborne outbreaks of viral disease have a greater impact among children than adults. To better quantify the impact on children, the literature hould be further reviewed for case studies of waterborne outbreaks where data are available on the resulting illness by age group. The EPA and/or Centers for Disease Control should attempt to collect these data as future outbreaks are documented.

Microbial risk assessment: don't forget the children.

Quantitative microbial risk assessment is a rapidly developing field with a purpose to quantify risks of infection, disease and mortality from the environmental exposure of pathogens. It is currently being applied to the development of standards for drinking water, wastewater re-use and foods. A growing body of evidence indicates that the greatest risk of infection for enteric pathogens is for persons less than 19 years of age. Children are more likely to become ill from consumption of contaminated drinking water and recreational activities. These increased risks may be because immunological, neurological and digestive systems are still developing. In addition, children are more environmentally exposed to pathogens. For some enteric pathogens children may be the greatest at risk population.

Chlorine and ozone disinfection of Encephalitozoon intestinalis spores.

Microsporidia are intracellular eukaryotic parasites which have the potential for zoonotic and environmental, including waterborne, transmission. Encephalitozoon intestinalis is a microsporidian pathogen of humans and animals and has been detected in surface water. It is also on the Contaminant Candidate List of potential emerging waterborne pathogens for the US EPA. We performed disinfection studies using chlorine and ozone on E. intestinalis spores with a cell-culture most-probable-number assay to determine infectivity. Chlorine experiments were performed at 5 degrees C at pH of 6, 7, and 8 with 1mg/L initial chlorine concentrations, while ozone experiments were performed at 5 degrees C and pH 7 with initial ozone doses of 1 and 0.5mg/L, both in buffered water. A derivation of Hom's model for disinfection kinetics under dynamic disinfectant concentrations was used to fit observed data and calculate concentration-time product (C*t) values. Chlorine C*t values varied with pH such that 99% (2-log(10)) C*t ranged from 12.8 at pH 6 to 68.8 at pH 8 (mg min/L). Ozone C*t values were approximately an order of magnitude less at 0.59--0.84 mg min/L, depending on initial concentration.

Development and optimization of a quantitative cell culture infectivity assay for the microsporidium Encephalitozoon intestinalis and application to ultraviolet light inactivation.

Microsporidia are unique parasites recognized as a major cause of intestinal illness among immunocompromised patients and occasionally in otherwise healthy hosts. These organisms have been detected in water and are likely transmitted by the fecal-oral route. The most common human pathogenic microsporidia for which cell culture methods have been established is Encephalitozoon intestinalis. This study describes the development of a quantitative cell culture infectivity assay for E. intestinalis and its application to assess inactivation by ultraviolet (UV) light irradiation. The method described here employs calcofluor white, a fluorescent brightener that targets the chitin spore wall, to visualize groups of developing spores in order to confirm infectivity. Serial dilutions of the spore suspension were seeded into tissue culture well slides containing RK-13 cells. Slides were then rinsed, fixed in methanol and stained with calcofluor white and examined microscopically. Large masses of developing spores were easily visible on infected cell monolayers. Positive and negative wells at each dilution step were used to quantify the number of infectious spores in the original suspension using a most-probable-number (MPN) statistical analysis. This assay was used to evaluate the disinfecting potential of ultraviolet light on E. intestinalis spores in water. The ultraviolet dose required for a 3-log(10) or 99.9% reduction in the number of infective spores was determined to be 8.43 mW s/cm(2).

Health effects of Acanthamoeba spp. and its potential for waterborne transmission.

Risk from Acanthamoeba keratitis is complex, depending upon the virulence of the particular strain, exposure, trauma, or other stress to the eye, and host immune response. Bacterial endosymbionts may also play a factor in the pathogenicity of Acanthamoeba. Which factor(s) may be the most important is not clear. The ability of the host to produce IgA antibodies in tears may be a significant factor. The immune response of the host is a significant risk factor for GAE infection. If so, then a certain subpopulation with an inability to produce IgA in the tears may be at greatest risk. There was no sufficient data on the occurrence or types of Acanthamoeba in tapwater in the U.S. Published work on amoebal presence in tapwater does not provide information on the type of treatment the water received or the level of residual chlorine. Assessment of the pathogenicity by cell culture and molecular methods of Acanthamoeba in tapwater would also be useful in the risk assessment process for drinking water. The possibility that Acanthamoeba spp. might serve as vectors for bacterial infections from water sources also should be explored. The bacterial endosymbionts include an interesting array of pathogens such as Vibrio cholerae and Legionella pneumophila, both of which are well recognized waterborne/water-based pathogens. Work is needed to determine if control of Acanthamoeba spp. is needed to control water-based pathogens in water supplies.

Outbreaks in drinking-water systems, 1991-1998.

During 1991-1998, 126 outbreaks, 429,021 cases of illness, 653 hospitalizations, and 58 deaths were reported in public and individual water systems in 41 states and three U.S. territories. A bacterial, viral, or protozoan etiology was identified in 41 percent of the outbreaks, and a chemical contaminant was identified in 18 percent. No etiological agent was determined in the remaining outbreaks. Important causes of outbreaks included contamination of untreated groundwater, inadequate disinfection of groundwater, and distribution system deficiencies, especially cross-connections and corrosive water. The responsible pathogen or chemical was identified in water samples collected during 31 percent of the reported outbreaks. Coliform bacteria were detected in water samples collected during the investigation of infectious-disease outbreaks in 83 percent of noncommunity and 46 percent of community water systems, but very few of these systems had exceeded the U.S. Environmental Protection Agency's maximum limit for total coliforms in the 12 months before the outbreak.

Removal of adenovirus, calicivirus, and bacteriophages by conventional drinking water treatment.

This study was conducted to evaluate the removal of adenovirus, feline calicivirus (FCV), and bacteriophages MS-2, fr, PRD-1, and Phi X-174 during conventional drinking water treatment using ferric chloride as a coagulant. Adenovirus and FCV were removed to a greater extent than PRD-1 and Phi X-174, indicating that these bacteriophages may be appropriate surrogates for both adenovirus and FCV. Of the four bacteriophages studied in the pilot plant, MS-2 was removed to the greatest extent (5.1 log), followed by fr (4.9 log), PRD-1 (3.5 log), and Phi X-174 (1.3 log). The virus removal trend in the pilot-scale testing was similar to the bench-scale testing; however, the bench-scale testing seemed to provide a conservative estimate of the pilot plant performance. In the pilot-scale testing, MS-2 and fr were removed with the greatest efficiency during filtration, whereas PRD-1 and Phi X-174 showed the greatest removal during sedimentation.

Efficacy of removal of CCL viruses under enhanced coagulation conditions.

The focus of coagulation as a water treatment process is shifting to accommodate recent regulatory additions that strive to balance the risks between microbial and chemical contamination of drinking water. In this work, enhanced coagulation using increased ferric chloride dose and/or pH adjustment was evaluated for removal efficacy of viruses on the United States Environmental Protection Agency (USEPA) Contaminant Candidate List (CCL), their surrogates, and dissolved organic carbon (DOC). Jar tests demonstrated that optimal DOC removal was achieved using 40 mg/L FeCl3 at a pH between 5 and 6. Under these conditions, bench-scale testing resulted in a maximum removal of 2.58 log units of adenovirus type 4, 2.50 log units of feline calicivirus, 2.32 log units of MS2, 1.75 log units of PRD1, 1.52 log units of phi-X174, 2.49 log units of fr, and 56% of DOC. The trend in virus removals (MS2 and fr > PRD1 and phi-X174) was consistent between bench- and pilot-scale testing; however, pilot-plant removals exceeded bench-scale removals. Feline calicivirus was more efficiently removed than the bacteriophages, thereby suggesting potential for the bacteriophages as suitable surrogates, with MS2 and fr being more representative and PRD1 and phi-X174 (which were removed to a lesser extent) more conservative. The bacteriophages do not appear to be appropriate surrogates for adenovirus.

Comparative inactivation of adenovirus serotypes by UV light disinfection.

The results of this study confirm that adenoviruses are the most resistant enteric viruses to inactivation by UV light and that adenovirus 40 appears to be the most resistant. The effect of freeze-thawing and storage in water may affect the sensitivity of some adenoviruses to inactivation by UV light.

Comparative inactivation of enteroviruses and adenovirus 2 by UV light.

The doses of UV irradiation necessary to inactivate selected enteric viruses on the U.S. Environmental Protection Agency Contaminant Candidate List were determined. Three-log reductions of echovirus 1, echovirus 11, coxsackievirus B3, coxsackievirus B5, poliovirus 1, and human adenovirus type 2 were effected by doses of 25, 20.5, 24.5, 27, 23, and 119 mW/cm(2), respectively. Human adenovirus type 2 is the most UV light-resistant enteric virus reported to date.

Removal of Encephalitozoon intestinalis, calicivirus, and coliphages by conventional drinking water treatment.

The removal of the Microsporidia, Encephalitozoon intestinalis, feline calicivirus and coliphages MS-2, PRD-1, and Fr were evaluated during conventional drinking water treatment in a pilot plant. The treatment consisted of coagulation, sedimentation, and mixed media filtration. Fr coliphage was removed the most (3.21 log), followed by feline calicivirus (3.05 log), E. coli (2.67 log), E. intestinalis (2.47 log), MS-2 (2.51 log). and PRD-1 (1.85 log). With the exception of PRD-1 the greatest removal of the viruses occurred during the flocculation step of the water treatment process.