Just 700 flu cases in NSW likely to still be active - Nov 20 2007

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Disease specialists estimate there are now only 700 active cases of equine influenza in New South Wales.

Epidemiologists, who study the patterns of diseases in populations, have been monitoring the flu outbreak closely, using information collected to report the situation and make predictions.

They say their findings provide strong encouragement that the disease is under control and eradication is achievable.

Some of their findings are shown in the two accompanying maps.

The infections are placed in one of three categories.

There are those under 21 days, which are deemed "recent" and still likely to be active. Those over 21 days are deemed "older" and are expected to be inactive. The third category is resolved, where officials have tested inactive areas and formally declared them disease-free.

Their research shows that the number of cases under 21 days old peaked late in September, and started to decline from about the second week of October to reach the current level of about 700 cases state-wide.

Numbers of older cases has 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 cases is starting to level off at around 5500 to 6000 as the number of recently reported IPs declines.

There have been a total of 73 newly infected premises identified during the last week, compared to 85 last week and 255 the week before that. The great majority of new cases have been in the purple zone, with additional cases in clusters at Wee Waa, Grenfell, Gunnedah, Armidale/Walcha, Dubbo and Parkes.

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 graph below shows that the EDR for horse flu has progressively declined since about mid-September and has been below 1 for most of the time since early October. The dotted lines show the 95% confidence limits for the estimate. The slight ups and downs of the EDR over time are probably due to variations in reporting over time.

"Although the EDR estimates are probably affected by some under-reporting, the graph provides strong encouragement that the disease is under control and eradication is achievable," the epidemiologists said.