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The human enterovirus group includes the polioviruses, coxsackieviruses, echoviruses as well as enteroviruses. They are ubiquitous and cause a wide spectrum of both common and uncommon illnesses.
Enteroviruses are shed in the upper respiratory tract for 1-3 weeks and in the faeces for up to 8 weeks after primary infection. the faecal-oral route is thought to be the predominant mode of enterovirus transmission.
Polioviruses are more resistant to many chemical disinfectants than the viruses that have a high lipid content (e.g. HIV). Studies have shown that standard cleaning and disinfection of endoscopes was totally effective against a heavy viral contamination and glutaraldehyde rapidly inactivated polio virus even when dried to a surface in serum.
The hepatitis B virus (HBV) which causes hepatitis B is a DNA virus from the Hepadnavirus family.
HBV is a hepatotrophic virus and causes an acute hepatitis after an incubation period that ranges between six weeks and six months. Following acute disease most people recover, the mortality rate being about 1% in hospitalised patients. Presentation of infection ranges from subclinical, which can be diagnosed only by laboratory tests, to fulminant liver diseases with necrosis and death.
HBV is transmitted in the health care setting by parenteral exposure to infected tissues, including blood or other body fluids. The virus may also be transmitted by exposure of mucous membranes, such as eyes, nose and mouth to infected material.
the risk of transmission of HBV following exposure to the blood of an infected person ranges from 2% if HBV e antigen (HBeAg) is absent, to 40% if HBeAg is present.
Standard precautions are sufficient to minimise the risk of transmission of HBV.
HBV is a highly infectious virus and high concentrations of viral particles are found in the blood of symptomatic hepatitis B sufferers and asymptomatic hepatitis b carriers, particularly those who are HBeAg positive. Despite the high infectivity of hepatitis B, there is only a single well-documented case of transmission of hepatitis B by endoscopy.
Clinical studies following up patients who have been endoscoped on the same endoscopy list as known hepatitis B positive patients have prodiced no evidence of infection. Hepatitis B virus is moderately sensitive to the majority of chemicals. However, failure to remove blood, mucous and protein coagulums will inactivate some chemicals. This means that the virus will be protected from the chemical's action.
The hepatitis C virus (HCV) is an RNA virus closely related to the Flavivirus group.
HCV is predominantly transmitted via contaminated blood. The risk of infection following needle stick injury with HCV positive blood is around 3%
Human body fluids including saliva, ascites and urine, all contain significant concentrations of HCV in infected patients.
Standard Precautions are the principal means of preventing transmission of HCV.
There is convincing evidence of transmission of HCV associated with endoscopic procedures, in many cases this seems related to inadequate cleaning. In most reports of endoscopic transmission of HCV there have been clear and gross deficiencies in the endoscope and accessory reprocessing.
At present the overwhelming evidence is that cleaning and disinfection protocols, when properly applied during endoscope and accessory reprocessing, will render instruments and accessories free of the risk of transmission of HCV. Failure to prevent endoscopic transmission of HCV has been due to wilful or inadvertent deficiencies in appropriate cleaning and disinfection protocols or (possibly) inadequate anaesthetic techniques.
The human immunodeficiency virus (HIV) is a blood borne retrovirus that was first recognised in 1981.
Between two weeks and several months following infection, seroconversion may result in an acute self-limited illness, similar to infectious mononucleosis, lasting for a week or two. Infected people may then be free of symptoms or clinical signs for many months to years before other clinical manifestations appear.
acquired immune deficiency syndrome (AIDS) represents the late clinical stage of infection with HIV, which most often results in progressive damage to the immune system, resulting in opportunistic infections and malignancies, constitutional and neurological disorders and other organ damage.
The concentration of HIV in the bloodstream is very high in the early stages of infection, including the window period between acquisition of HIV and the seroconversion illness. After the resolution of this illness, HIV viral load decreases due to host immune responses and stabilises at a lower level. As immunodeficiency progresses and AIDS develops the HIV viral load rises again. Viral load is also influenced by antiretroviral therapy. Most patients on combination antiretroviral therapy have low HIV viral load.
Infectivity is believed to begin shortly after primary infection and continue throughout life, irrespective of whether the patient is symptomatic. Infective HIV particles are present in the blood, semen and other body fluids of infected individuals.
HIV is a blood borne and sexually transmissible virus. HIV may be transmitted by direct contact with blood or other body fluids, through mucous membranes, nonintact skin or through percutaneous injury. Needle stick injury with HIV positive blood has resulted in sero-conversion ranging from 0-0.42% in various studies.
Standard precautions are sufficient to prevent HIV transmission.
Additional precautions for patients with HIV are required only for those patients with opportunistic infections such as pulmonary tuberculosis.
HIV is sensitive to many chemical disinfectants including aldehydes. A variety of studies have shown that when the virus is protected within a dried protein coagulum, some chemical disinfectants including 1% glutaraldehyde will fail to inactivate the virus within 5 minutes. However, in another series of studies in which the surface and internal channels of endoscopes were contaminated with high titre HIV serum, simple manual cleaning removed HIV activity from all except a single endoscope. The remaining viral activity was removed from this endoscope after 10 minutes or less in 2% glutaraldehyde.
Where endoscopes were sampled after removal from HIV positive patients, all HIV present on endoscopes was removed by manual cleaning alone. This emphasises the absolute necessity to ensure that scrupulous manual cleaning removes all traces of blood and proteinaceous material. such cleaning should be undertaken without delay.
To date there has been no unequivocal demonstration of transmission of human immunodeficiency virus by gastrointestinal endoscopy. The extremely long incubation time for clinical AIDS would however make the detection of a very isolated instance of HIV transmission difficult to detect.
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