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Fresh equine flu cases in rapid decline

December 4, 2007

New South Wales now has just 200 infected properties where the disease is still likely to be active.

A recent report on the epidemic shows the state is on track to eradicate the disease.

NSW DPI epidemiologists are monitoring the equine influenza outbreak closely, using information collected to report the situation and make predictions.

The areas that the state has moved to green zones in recent weeks means that the status of 1479 previously infected properties have been resolved.

While the great majority of properties remain to be cleared - there are more than 5000 (shown in the graph in blue) - the infections are all more than 21 days old and are no longer likely to be contagious.

Recent cases - those under 21 days old (shown in the graph in red) - are still considered active.

"As can be seen," the state epidemiologists said in a report, "the number of recent cases reached a peak in late September, started to decline from about the second week of October and is now about 200 [recently infected properties] state-wide.

"Numbers of older cases have increased progressively since late September. Increasing numbers of cases have now been resolved, with work progressing to actively resolve cases, particularly in outlying areas and clusters."

The total number of infected properties is starting to level off at around 5500 to 6000 as the number of recently reported infected properties declines.

The figures show that the numbers of new cases increased rapidly in the first few weeks, reaching a peak of about 1000 new infected properties in the fourth week (late September).

Numbers of new infected properties have declined substantially since about week seven, to about 50 a week since early November (week 11).

Just 51 newly infected premises have been identified in the last week, compared to 55 the week before. All new cases have been in existing infected areas, including cases at Grenfell, Narrabri, Armidale/Walcha, Parkes/Forbes and in parts of the purple zone. No new outlying cases have been identified in the last week.

The estimated dissemination rate (EDR) for a disease is the average number of new cases generated by each existing case. An EDR of greater than 1 indicates that the disease will continue to spread and the epidemic will continue. Conversely, an EDR of less than 1 means that the epidemic will gradually die out.

The EDR for horse flu has progressively declined since mid-September and has been below 1 for most of the time since early October.

This, the epidemiologists say, provides "strong encouragement" that the disease is under control and eradication is achievable.



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