A number of cases of the potentially fatal infection tuberculosis (TB) are being investigated by a health board.
Betsi Cadwaladr University Health Board's (BCHUB) executive director of public health, Teresa Owen, said the infection has made an "unwelcome comeback" in recent decades.
Ms Owen said a team is investigating some recent cases in Wrexham among people who are homeless.
She said in a report, more cases are expected to "come to light".
Tuberculosis is a bacterial infection spread through inhaling tiny droplets from the coughs or sneezes of an infected person.
Ms Owen said the infection has returned in dangerous forms such as multi-drug resistant (MDR) and extremely drug resistant (EXDR) strains.
There were 19 cases of TB the BCHUB area in 2018, 10 of which were in Wrexham county, up from six the year before, the Public Health Annual Report for 2019 said.
Ms Owen said: "TB more often affects people with complex health and social needs, who may find it harder to access appropriate services.
"This can make it very challenging to successfully find and treat people with TB.
"Many of the recent cases have complex social needs, including homelessness and substance misuse.
"Due to the lengthy incubation period of TB and the social context of the cases to date, it is likely that further cases will come to light as the investigations continue."
The board's health protection team have been working closely with the respiratory team in Wrexham to investigate cases.
Ms Owen's report will be considered by Betsi Cadwaladr University Health Board later.