Waterborne Disease Outbreaks. Occurrence in Sewage and Water

Adenoviruses have been responsible for numerous out­breaks within facilities for children (e.g., day care centers, schools, orphanages, and camps), within hospitals, health­care centers, and among military personnel. Since all serotypes of adenovirus (besides enteric alone) are excreted in feces, contaminated water could be a source of exposure for any type, either through ingestion, inhalation, or by direct contact with the eyes.

Contact with recreational water has been associated with numerous adenovirus outbreaks over the years. Ade­noviruses are the most reported cause of swimming pool outbreaks associated with viruses. Many outbreaks of PCF from nonenteric adenoviruses have come from people swimming in pools and lakes. Adenovirus types 3, 4, 7, and 14 have been associated with outbreaks in swimming pools and have been detected in pools.

There have been three drinking water outbreaks reported in Europe in which enteric adenoviruses may have been a cause of gastroenteritis. Multiple viral agents were involved and the water had not been ade­quately disinfected. No food-borne outbreaks have been documented.

Occurrence in Sewage and Water. Adenoviruses are commonly detected in raw and non- disinfected secondary sewage discharges, although little published data are available for the United States. Entero­viruses are removed to a greater extent than adenoviruses by activated sludge. Likewise, when comparative studies have been conducted, adenoviruses usually outnumber enteroviruses in surface waters.

To date, there appear to have been no real attempts to determine the occurrences of adenoviruses in groundwater, although other enteric viruses have been detected in several studies in the United States. Nonetheless, adenovirus was one of the likely causes of a drinking water outbreak in Finland. This indicated that adenovirus might be expected to be present in sewage-contaminated groundwater.

Survival in the Environment.Limited data suggest that adenoviruses survive longer in water than enteroviruses and hepatitis A virus. Adeno­viruses also exhibit greater thermal stability than enter­oviruses. This may explain their longer survival in water. They are capable of surviving for months in water, espe­cially at low temperatures.

The double-stranded DNA that makes up the genome of the virus may provide more stability in the environment. In addition, adeno­viruses may use host cell repair enzymes to repair dam­aged DNA. This may also prolong their survival in the environment and enhance their resistance to inactivation by ultraviolet (UV) light.

Resistance to Disinfectants.Only limited studies have been performed on the sensi­tivity of adenoviruses to disinfectants commonly used in water treatment. These studies suggest that adenoviruses have equal or greater sensitivity to oxidizing disinfectants (e.g., chlorine) than other enteric viruses (e.g., hepatitis A virus); however, they are the most UV-light-resistant, waterborne pathogens known.

They are more resistant to UV-light disinfection than waterborne viruses with single- and double-stranded RNA genomes. The adeno­virus genome comprises double-stranded DNA. This allows the virus to use host cell repair enzymes to repair damage in the DNA caused by UV light.

Only one strand of the nucleic acid may be damaged during UV-light disinfection. The undamaged strand may then serve as a template for host cell repair enzymes. The presence of host cell repair enzymes enables DNA viruses to repair the damage caused by UV light. Adenovirus type 40 requires a dose of 226mJ/cm² for a 99.99% inactiva­tion of the original concentration while poliovirus type 1 (a single-strand RNA genome) only requires a dose of 31 mJ/cm² (Thurston-Enriquez et al., 2004).

Summary.Adenoviruses cause a wide variety of illness in humans, but are largely associated with respiratory illnesses and gastroenteritis. While these infections are often mild and self-limiting they can cause serious mortality in the immunocompromised.

They are the most plentiful enteric virus found in sewage or fecally contaminated waters and have been regularly associated with infections associated with swimming pools where disinfection levels have not been properly maintained. While fairly susceptible to common water disinfectants they are the most resistant waterborne agents known to UV-light disinfection.