Infection Transmission Routes

Federal, state, and local health agencies publish rules and guidelines that dehne isolation procedures. Healthcare organizations should follow these guidelines because infectious agents can be transmitted by several routes  

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List the six types of disease and infection transmission routes. 

The hepatitis C virus can be transmitted parenterally or sporadically. Risk groups with a high prevalence rate are haemophiliac patients (70-90%), i.v. drug addicts (50-90%), posttransfusion patients (60-80%), dialysis patients (5-30%) and liver transplant recipients. In 40-50% of patients with a positive anti-HCV test, the transmission route is still unknown. These cases are designated community-acquired or sporadic hepatitis C. The cause is rooted in poor hygienic conditions and close physical contact. Ill, 211, 334) Fundamentally, the possibility of infection depends on the virus titre in the source person - it is considerably lower than with HBV infection. Nosocomial infection between patients has also been observed. (281, 329, 390)... 

The transmission route of HDV corresponds to all the channels of infection of HBV, since its pathogenicity is coupled to the HBV as a helper virus. Thus HDV is mainly transmitted parenterally through blood and blood products as well as by sexual and even close physical contact. HDV infection cannot survive HBV infection. (417, 434,443,444, 452, 453)... 

Pending identification of type thereafter dictated by transmission routes for specific infecting agent... 

The transmission route vary according to the endemicity rates. In areas of high endemicity, the most common route of transmission is perinatal or the infection is acquired horizontally during the preschool years. Lin et al. (2(X)3) demonstrated that the prevalence of HBeAg is higher in Asian than in African HBsAg carrier mothers (40% versus 15%), so perinatal transmission is greater in Asians, but mainly horizontal in Africans. In areas of intermediate endemicity, transmission is either perinatal or horizontal as also mentioned by Mele et al. (2001). 

The endemicity, transmission routes and the age being infected is summarised in Table 1. 

Generally speaking, infection transmission occurs via three routes contact, air and water. Advances in molecular detection methods and sampling techniques for viruses, bacteria and fungi have enabled researchers to identify the exact strain and source of infections, and thereby develop a better understanding of transmission (Ulrich etal, 2008). Contact is widely considered the most frequent transmission route, but in practice all three routes may interact in the spread of nosocomial infections. Waterborne transmission is a serious problem in some circumstances, but there are few studies on prevention and we will not consider it further here. 

Although airborne transmission poses serious safety risks, contact contamination is generally recognized as the principal transmission route of nosocomial infections, such as MRSA and C difficile, which survive well on surfaces and other reservoirs (Bauer et al., 1990 lOM, 2004). Healthcare workers hands play a key role in both direct and indirect transmissions. A staff member may touch two patients in succession without washing his or her hands, or touch an environmental surface or feature after direct contact with an infected patient, which in turn contaminates the hands of someone else (Ulrich and Wilson, 2006). Because MRSA can survive for weeks on environmental surfaces, these surfaces can themselves become the source of new outbreaks. 

Fig. 4.1 Routes of infection and spread of transmission of disease. CNS, central nervous system.

Propagated outbreaks of infection relate to the direct transmission of an infective agent from a diseased individual to a healthy, susceptible one. Mechanisms of such transmission were described in Chapter 4 and include inhalation of infective aerosols (measles, mumps, diphtheria), direct physical contact (syphilis, herpes virus) and, where sanitation standards are poor, through the introduction of infected faecal material into drinking water (cholera, typhoid). The ease oftransmission, and hence the rate of onset of an epidemic (Fig. 16.3) relates not only to the susceptibility status, and general state of health of the individuals but also to the virulence properties of the organism, the route oftransmission, the duration of the infective period associated with the disease. 

Measles, mumps and rubella (German measles) are infectious diseases, with respiratory routes of transmission and infection, caused by members of the paramyxovirus group. Each virus is immunologically distinct and has only one serotype. Whilst the primary multiplication sites of these viruses is within the respiratory tract, the diseases are associated with viral multiplication elsewhere in the host. 

Prior to routine screening of blood products in the early 1990s, the primary route of transmission of the HCV was blood transfusions, when the risk was 0.02% per unit transfused. Since then, the risk has decreased significantly (0.001% per unit transfused).13 Today, intravenous drug users utilizing contaminated paraphernalia are responsible for most HCV transmission. Other populations at risk for acquiring HCV are listed in Table 21-1. Approximately 10% of the individuals infected with HCV have no identifiable risk factors. 

Hepatitis E is similar to hepatitis A in that the mode of transmission is via the fecal-oral route. Therefore, the most effective ways to prevent acquiring the virus are good personal hygiene and proper disposal of sanitary waste. Frequent handwashing and avoiding contaminated foods and vegetables decrease the risk of infection. 

Normal routes of transmission Windborne Contact (introduction of infected seeds). Secondary Hazards Mechanical vectors (windblown rain) Spores. 

HAV infection primarily occurs through transmission by the fecal-oral route, person-to-person, or by ingestion of contaminated food or water. The incidence of HAV correlates directly with low socioeconomic status, poor sanitary conditions, and overcrowding. Rates of HAV infection have increased among international travelers, injection drug users, and men who have sex with men. 

Medical Classification, Probable Form of Dissemination, Detection in the Field, Infective Dose, Incubation Time, Persistence, Personal Protection, Routes of Entry to the Body, Per-son-to-Person Transmissible, Duration of Illness, Potential Ability to Kill, Defensive Measures, Vaccines, Drugs Available, and Decontamination. In each case, for both Chemical and Biological agents, each agent will have guidelines laid out within the book. 

Infection by PrPSc is a more challenging—and obscure—process. Pathogens in mammals not only have to spread within an infected organism but also they must spread from one organism to another. The route of transmission followed by PrPSc is more complicated than that of fungal prions and places more requirements on this system. Tissues other than brain are also involved (Aguzzi, 2003 Seeger et al., 2005). 

Actually, in some South American regions (e.g., the Brazilian Amazon), T. cruzi infection by oral route is the most important mode of Chagas disease transmission. 

The importance of transmission via the oral route has long been known in the case of susceptible omnivorous or insectivorous animals, which feed on vector insects and infected animal reservoirs (Dias, 2006 Neto et ah, 2000). Some authors consider the possibility that Carlos Chagas, in his first study together with Oswaldo Cruz, played an important role in the first demonstrated case of oral transmission of Chagas disease. Marmosets (C. penicillata) were placed in cages together with insects infected by the parasite, and also acquired the parasite. It is now known that transmission to these animals by insect bites is rare, and, at the time of the experiment, no entrance points were found on the animals thus, the hypothesis of ingestion of the insects by the marmosets cannot be discarded (Coura, 1997 Dias, 2006). 

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