Tuesday, August 9, 2011

Hospital acquired Respiratory viral infections

A.   Respiratory syncytial virus.
B.   Influenza viruses.
C.   Parainfluenza viruses.
D.   Adenoviruses.
E.    Rhinoviruses
They are increasingly recognized as significant pathogens; given the relative ease with which they spread and their relatively short incubation time (1-8 days), these viruses can result in significant nosocomial problems.
Transmission occurs via either small droplet; by coughing, sneezing, or talking and is readily transmitted over considerable distance; or large droplets for which transmission usually only follows close person to person contact and results from direct inoculation of virus-laden droplets onto the mucous membranes (e.g., eyes and nose) of susceptible host. Autoinoculation results from transfer of virus from hands to mucous membranes. Transmission between patients on the hands of health care workers may occur if there is failure to wash hands between patients. While most nosocomial infection occur throughout the year, the peak incidence of transmission of respiratory viruses occurring in the winter months .
A.   Respiratory Syncytial Virus (RSV):
RSV is belonging to the family Paramyxoviridae, it is nonsegmented negative-strand RNA , and the most important cause of lower respiratory tract illness in infants and young children worldwide. RSV may produce croup, bronchitis, bronchiolitis, or pneumonia. It is most common cause of respiratory disease in hospitalized infants < 1 year of age .
It has been reported to be responsible for approximately 45% of all hospital admissions for acute respiratory disease in age under 2 years. Bronchitis and pneumonia are the most common manifestations. However, immunity to reinfection is not permanent, older children and immunocompetent adults developing recurrent episodes of mild upper respiratory tract infections through out life. RSV spread by close contact with respiratory secretions, via large droplets or fomites or unwashed hands of health care workers or relatives or contaminated environment. It can persist on skin and porous surfaces as gowns and papers for up to 30 minutes and up to 6 hours on nonporous surfaces e.g., gloves and countertops. Small droplets spread can occur less commonly when the source and recipient are in close contact.
This viral infection is a major cause of nosocomial infection; careful attention to the principle of infection control is essential. Good laboratory diagnosis is needed not only for treating patients, but also for limiting nosocomial spread. 
B.   Influenza virus:
It belongs Orthomyxoviridae family. It has three types Influenza virus A, B, and C. All Influenza viruses have segmented negative sense RNA core surrounded by a lipid envelop. The A and B types are distinguished by two glycoproteins, hemagglutinin (HA) and neuraminidase (NA), that protrude from the virion surface. Influenza C virus contains only one glycoprotein, hemagglutinin-esterase fusion protein.
Influenza viruses are highly infectious, transmitted in both large and small droplets but mainly by large droplets (> 5 um) depositing into the mucosal surfaces of eyes, mouth, respiratory tract and hands. Small droplet spread accounts for the explosive nature of influenza outbreaks in closed environments. Numerous nosocomial outbreaks involving medical, pediatric and bone marrow transplantation (BMT) units have been reported.
Novel influenza A (H1N1) which called swine influenza transmitted from pig to human. Once a human become infected can spread the virus to other human presumably in the same way as seasonal influenza is spread (Bronze, 2009) through large, small droplets and also contact with contaminated surfaces. Its incubation period is unknown and could range from 1-7 days, and more likely 1-4 days. The clinical findings are cough, sore throat, rhinorrhea, and shortness of breath, myalgia, fatigue, vomiting or diarrhea. Groups at high risk are children <5 years, person aged 65 years or older, pregnant women, adults and children with chronic pulmonary; cardiovascular; haematological; neurogenic or metabolic disorders; and who have immunosuppression ( by medications or HIV), residents of nursing homes and other chronic care facilities (CDC, 2009).
C.   Para influenza  virus (PIV):
It is a genus in Paramyxoviridae family. These viruses have features that distinguish them from other members of paramyxoviridae. They possess both hemagglutinating and neuraminidase activities on their receptor- binding protein and all have the ability to encode a nonstructural C protein. Like all other members of paramyxoviridae, these viruses although pleiomorphic, are roughly spherical in shape, about 150-400 nm in diameter and possess a lipid envelope. All contain a single stranded RNA.
There are 4 types of human PIV, with types 1, 2, and 3 being the most important. They are the major cause of laryngotracheobronchitis (croup) in children and are also responsible for upper respiratory tract infections (types 1, 2 and 3) and bronchiolitis / pneumonia (type 3). Typically, infections with parainfluenza virus types 1 and 2 occur in the autumn, and type 3 infections occur throughout the year.
          There is evidence to suggest that outbreaks are more likely to be due to transmission between patients rather than the continuous reintroduction of different strains by staff or visitors (Karron et al., 1993). Transmission of these viruses by direct contact with respiratory secretions via fomites or large droplet spread is the main route. Survival of the viruses for up to 10 hours on non absorptive surfaces (Stainless steel) and 4 hours on absorptive ones (gowns) has been reported. However survival on finger pads is poor, with only 5% of the virus being recoverable after 10 minutes .
D.   Adenoviruses:
Four families are now recognized, These are Mastadenoviridae isolated from mammals (human, bovine); Aviadenoviridae isolated from birds (duck, goose, turkey); Atadenoviridae isolated from some bovines, birds and snakes and Siadenoviridae isolated from frogs, fish and turkeys giving a total of at least 170 different viruses.However, the most intensively studied adenoviruses are the 51 serotypes isolated from human. 
                                           Adenivrus structure
Adenoviruses are non enveloped, 80 nm in diameter double stranded DNA genome, and their capsids have ichosahedral shell made up of 252 capsomeres, 240 hexon capsomeres and 12 penton capsomeres. Pentons have antenna like projections which vary in length depending on subtype of virus.
Adenoviruses differ from the other community – acquired respiratory viruses because they can be acquired both exogenously and endogenously, following reactivation. There are different serotypes causing a range of syndromes, including acute respiratory disease, epidemic keratoconjunctivitis and pharyngoconjunctival fever. Fecal-oral transmission also occurs and accounts for cases of sporadic diarrhea seen
in children. Adenoviruses are highly stable and can be transmitted via large droplets and also via small aerosol droplets. Nosocomial adenovirus infections have been well described and can affect both patients and staff. A fatal case of disseminated adenovirus infection in an immunocompromised patient resulted in 38 staff members becoming infected.
  Those in the intensive care unit were at highest risk, probably as a result of direct contact with respiratory secretions following intubation, although prolonged contact with the patients was also important. Large outbreaks of epidemic Adenovirus related keratoconjunctivitis in ophthalmology clinics have been reported. Using restriction enzyme analysis; a point source is usually identified, with virus being transmitted on the hands of health care workers or via infected equipment, e.g., tonometer heads (Takeuchi et al., 1990).
A.   Rhinovirus:
Rhinovirus genus of the Picornavirus family is one of the causative agents of the common cold and comprises > 100 serotypes. These viruses share a number of characteristics, including small size, icosahedral morphology, and lack of lipid envelope so resist inactivation by organic solvents, single stranded RNA genome and general arrangement of their structural proteins.
Typical symptoms include coryza, sneezing, lacrimation and chilliness and last from 2-7 days. No fatalities have been reported, but these infections may predispose individuals to more serious complications such as sinusitis, otitis media, and asthma. A report has suggested that pneumonia may follow an upper respiratory tract rhinovirus infection in BMT patients.
These viruses are readily transmitted following close contact with infected respiratory secretions, transmitted by contaminated hands carrying virus to the mucous membranes of the nose or eye. There is evidence supporting the role of aerosols in the transmission of the virus. Hand washing is the most effective way of minimizing transmission. Large and small – droplet precautions should be used in outbreak situation to control spread.

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