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					Severe Acute Respiratory Syndrome (SARS)

Prof. A.L.Sharma

Introduction
Severe Acute Respiratory Syndrome (SARS) is a newly emerged disease which has its origins in Guangdong Province, China. The earliest known cases were identified in midNovember 2002. Since then, probable cases of SARS have been reported in 17 countries.

The current cumulative number of cases of SARS is 2781 cases with 111 deaths, officially notified to WHO.

It is a respiratory disease of man which is caused by the SARS corona virus (SARS-CoV). There has been an outbreak of almost pandemic proportions , between November 2002 and July 2003, with 8,096 known infected cases and 774 deaths worldwide. ( A case-fatality rate of 9.6%).

In early 2003 within a matter of weeks SARS spread from the Guangdong province of China rapidly infecting individuals in about 37 countries around the world.

Signs and symptoms
Initial symptoms are flu-like and may include: fever, lethargy, myalgia, gastrointestinal symptoms, cough, sorethroat and other non-specific symptoms. The only symptom that is common to all patients appears to be a fever above 38˚C (100.4˚F). Shortness of breath may follow.

Agent Factors
SARS is caused by coronavirus named as SARS-CoV, Virus is stable in faeces and urine at room temperature for at least 1-2 days. It is stable for up to 4 days in stool from patients with diarrhoea because of its higher pH compared to normal stool.

SARS-CoV has been isolated from stool after 36 hours from a paper, a Formica surface and a plastered wall . After 72 hours, on a plastic and stainless steel surface , and
After 96 hours on a glass slide.
•

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Virus loses infectivity after exposure to different commonly used disinfectants and fixatives. Heat at 56°C rapidly kills approximately 10 000 units of SARS-CoV per 15 minutes.

CoronaVirus ‘SARS CoV’

CoronaVirus ‘SARS CoV’

Reservoir of Infection Apart from clinical cases ,evidence is emerging that subclinical cases may form a major reservoir. There is evidence that natural infection with SARS-CoV may occur in a number of animal species indigenous to China and parts of south-east Asia.

In Hong Kong SAR and Shenzhen, China announced the results of a joint study of wild animals taken from a market in southern China selling wild animals for human consumption. The study detected several coronaviruses closely related genetically to the SARS coronavirus in two of the animal species tested (masked palm civet and raccoon dog).

The study also found that one additional species (the Chinese ferret badger) elicited antibodies against the SARS-CoV. These and other wild animals are traditionally considered delicacies and are sold for human consumption in markets throughout southern China.

Wild Life Reservoirs of SARS ?

Chinese ferrer badger

masked palm civet

Wild Life Reservoirs of SARS ?

raccoon-dog

Domestic Animals & Pets Rodent droppings collected during the Amoy Gardens investigation in Hongkong have tested PCR positive.
However, there is no laboratory evidence that rodents can be infected;

`

SARS-CoV was detected on the body surface and gut contents of cockroaches by PCR but their organs were negative.
Cockroaches may act as mechanical vectors of virus transmission.

Incubation Period Estimates of Incubation Period are derived from an analysis of SARS cases with single point exposures or exposure over a well-defined interval. Most countries reported a median incubation period of 4-5 days, and a mean of 4-6 days.

The minimum reported incubation period of 1 day was reported from China and Singapore and the maximum of 14 days was reported by China. It is unclear whether the route of transmission has any influences on the incubation period.

Period of infectivity Maximum virus excretion from the respiratory tract occurs on about day 10 of illness and then declines.
Transmission efficiency appears to be greatest from severely ill patients or those experiencing rapid clinical deterioration, usually during the second week of illness.

• In Singapore stool samples were found to be PCR positive by days 12-14 and then the detection rate declined. • In Honkong 22% of stools tested by RT-PCR were positive on days 0-2 of illness, peak to 100% on 12-14th day and fells to 50% by 21st – 23rd day.

Routes of transmission
Available evidence suggests that SARS emerged in Guangdong Province, in southern China in November 2002. More than one third of early cases, with dates of onset before 1 February 2003, were in food handlers. (persons who handle, kill, and sell food animals, or those who prepare and serve food).

SARS appears to be spread most commonly by close person-to-person contact involving exposure to infectious droplets, and possibly by direct contact with infected body fluids.

Case Fatality Ratio
The case-fatality ratio of SARS is estimated to range from 0% to more than 50% depending on the age group affected. WHO estimated a crude CFR of 14% in Singapore and 15% in Hong Kong SAR. in some Centres, most SARS deaths occurred among the elderly,

Host Factors
People at high risk of acquiring infection Multivariate analysis of risk factors associated with SARS-related mortality from Hong Kong shows

a) b) c) d)

Increasing age, male sex, presence of co-morbidity and health care seeking behaviour. as important predisposing factors

Most SARS cases have occurred in young adults.
On the basis of present data, children appear to be less likely to present with SARS than adults.

Human Mobility particularly International Air Travel has played an important role in the spread of the infection. There has also been limited transmission associated with air travel.

The care and slaughter of wildlife for human consumption in the wet markets of southern China is associated with serological evidence of infection. The transmission of SARS in the Metropole Hotel and the Amoy Gardens has been attributed in part to environmental contamination, with a possibility of insect vector contributing to the spread.

•

SARS may be suspected in a patient who has:Any of the symptoms, including a fever of 38 °C (100.4 °F) or higher, and Either a history of: – Contact (sexual or casual) with someone with a diagnosis of SARS within the last 10 days OR

Diagnosis

Travel to any of the regions identified by the WHO as areas with recent local transmission of SARS A probable case of SARS has the above findings plus positive chest X-ray findings of atypical pneumonia or respiratory distress syndrome.

A chest x-ray showing increased opacity in both lungs, indicative of pneumonia, in a patient with SARS.

With the advent of diagnostic tests for the coronavirus probably responsible for SARS, the WHO has added the category of "laboratory confirmed SARS" for patients who would otherwise fit the above "probable" category who do not (yet) have the chest x-ray changes but have positive laboratory diagnosis of SARS based on one of the approved tests (ELISA, immunofluorescence or PCR).

Control
Attempts were made to control further SARS infection through the use of quarantine. In Singapore, schools were closed for 10 days and in Hong Kong they were closed until 21 April to contain the spread of SARS.

On 27 March 2003, the WHO recommended the screening of airline passengers for the symptoms of SARS. Barrier Nursing

Vaccines
SARS vaccines are being developed and trials are under way


				
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posted:7/24/2009
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