She was in her 20s, and fighting a debilitating fatigue that came with constant viruses and infections. But despite multiple sinus surgeries, long stints on strong antibiotics, and allergy treatments, her doctors were stumped.

"Everyone was wondering why I wasn't getting better," she said.

She had to take a lot of unpaid sick leave. On Wednesdays, she would sleep.

"I just remember thinking, this isn't normal," she said.

"I couldn't get off antibiotics. Serious, strong antibiotics. The infection just wouldn't clear. We'd addressed the structural issues with four different surgeries. I'd be on antibiotics. And every time I'd stop them I'd get the infection back immediately. By the time I was 34, someone finally thought to check whether I had a primary immunodeficiency [PID], and I did."

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Having that diagnosis was a game-changer. She began monthly intravenous immunoglobulin therapy, which was "incredible", and has since begun weekly subcutaneous immunoglobulin infusions at home.

"It has changed my life," she said. "I don't get as sick as often, and I don't get those same chronic sinus problems. The weekly therapy is a lot more stable. Not as many ups and downs. I used to joke I'd get 20 good days and eight crappy ones. But I've also got more control now. I've gone from having to work part time to full time.

"I'm not 100 per cent, but life is peaches and cream to how I felt before."

Ms Smith, now 44, said she was lucky in that her symptoms didn't kick in until after she was educated and had clocked some years of work experience.

"If I hadn't been in that position I don't think I'd have the career I do now," she said. "It could really impact a young person's life trajectory."

She believes an earlier diagnosis could also help address the impact the condition can have on family and social roles.

"I'm a woman in my 40s and my 70-year-old mum looks after me rather than the other way around," she said.

Ms Smith shared her story as the Australasian Society for Clinical Allergy and Immunology (ASCIA) launched its strategy to educate health professionals to recognise early warning signs of PID, improve access to paediatric and adult clinical immunology/allergy specialists, and campaign for equitable access to testing and treatments.

Primary immunodeficiency disorders are a diverse group of more than 400 potentially serious, chronic illnesses that can lead to frequent or severe infections, swellings and autoimmune problems.

ASCIA said it had been estimated that between 70 and 90 per cent of people are still undiagnosed worldwide with PIDs, which affect adults as well as children.

The society said Victorian data showed that in adults the average delay from symptom onset to diagnosis is eight years, and every year of delay costs life expectancy.