A van driver is today in a satisfactory condition in hospital after developing a suspected case of Legionnaire's Disease.
The man, in his 50s, has responded well to treatment and no other cases have been reported.
The patient, who lives in the Shoreham area, is being treated at Worthing Hospital.
Tests have been carried out but it could take up to 14 days before the results are known.
Public health officials are trying to trace the source of the potentially-fatal bug but it is believed to be a one-off case.
A spokesman for Adur, Arun and Worthing Primary Care Trust said: "We believe this is an isolated incident and we are advising people there is no need to worry.
"Cases of the disease are very rare with usually about 200 cases across the country every year."
The bug cannot be spread from person to person. It is contracted through inhaling tiny droplets of water, often via air conditioning and water systems, and is treated with antibiotics.
For advice, call the NHS Direct helpline on 0845 4647, or via its web site www.nhsdirect.nhs.uk
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