A Fulton Hogan employee who has contracted type C meningococcal disease was in the same meeting last week as Fulton Hogan chief executive Bill Perry, who died over the weekend.
Public health staff are investigating whether there is a link between three South Island cases of type C meningococcal disease.
Mr Perry, 48, died on Saturday, after he was taken to Christchurch Hospital that morning.
Another Fulton Hogan employee has also contracted the same strain.
Canterbury medical officer of Health Alistair Humphrey said the man, in his 50s, had been at the same company meetings as Mr Perry last week.
"As a precaution, all other attendees of the meeting and those in direct contact with them have been administered treatment and advised of the symptoms of meningococcal disease," he said.
"Canterbury and Southern District Health Boards are closely monitoring the situation."
Another person, a woman in her 40s, has also contracted the strain and is in Christchurch Hospital.
She is not believed to have any connection to the men, although Public Health Staff are investigating whether there was a link between all three cases.
A baby hospitalised in Dunedin had been believed to have the same strain, however instead has the unusual W135 strain.
Public Health South medical officer of health Dr Marion Poore said an "error" lead to reports it had the C strain, and the case is not related to the others.
The baby has since been discharged and has made a full recovery.
Mr Humphrey said Mr Perry may not have been the source of the strain.
"Meningococcal C characteristically affects young adults not people in their middle age, so one of the lines we are looking at is whether or not there is another source to this illness," he told Radio New Zealand.
"It might be through some teenagers getting together over the holidays."
Mr Humphries said the diseases is contracted through "droplets spread" sharing food, drinks or sneezing.
He said the symptoms were "vague", such as bad headaches, stiff necks, and lights becoming unpleasant.
Doctors are warning anyone who has come in contact with someone with the disease to see a doctor immediately or call the 24-hour Healthline on 0800 611-116.
Case 1: Fulton Hogan CEO Bill Perry contracts meningococcal disease and dies on Saturday.
Case 2: Another Fulton Hogan employee is admitted to Dunedin Hospital on Monday.
Case 3: Baby in Dunedin Hospital with the same strain.
Case 4: Woman in her 40s in Christchurch Hospital with the same strain.