Public health officials are playing catch-up with a potentially fatal disease they believe millions of baby boomers have been carrying around for decades without realizing they are sick.

This summer, the U.S. Preventive Services Task Force issued a statement asking everyone between age 45 and 65 to get tested for hepatitis C, a blood-borne pathogen that attacks the liver and kills 15,000 people a year. People in this age group should get tested even if they otherwise think they are in perfectly good health, according to the Preventive Services Task Force.

“The majority of people who have hepatitis C don’t realize they are sick,” said Ann Thomas, a public health physician with the Oregon Health Authority’s acute and communicable disease prevention program.

During the 1980s, public health officials witnessed a rash of hepatitis cases where people started exhibiting symptoms of chronic liver disease after they got a blood transfusion but showed no signs of a hepatitis A or hepatitis B infection. Both of these infections can be prevented with a vaccine.

They got the answer to their question in 1989 when a group of scientists published a paper identifying a third hepatitis virus — hepatitis C — that according to the U.S. Centers for Disease Control and Prevention was responsible for about 200,000 new hepatitis infections a year at its peak in that decade.

Public health officials responded to this discovery by developing a procedure that screened any blood sample used in a transfusion for the pathogen so it was not inadvertently passed on to someone else.

They also identified risk groups — people who used intravenous drugs make up about 60 percent of hepatitis C cases, while those who engage in risky sexual behaviors make up 20 percent — and encouraged them to get tested regularly.

These steps proved to be effective.

According to a report on the CDC’s website, the disease’s nationwide incidence rate decreased from its peak in the 1980s to 25,000 new cases in 2001 and an estimated 16,000 new cases in 2009.

More current data could not be obtained from the federal agency because of the ongoing government shutdown.

The Oregon Health Authority’s public health division made reporting new cases of chronic hepatitis C a mandatory requirement in July 2005. Since then, the state’s total number of new cases increased steadily until it saw its peak of 6,692 cases, including 203 that were reported by health care providers in Crook, Deschutes and Jefferson counties in 2008. The state’s total number of cases dropped to 4,660 — 275 were in Central Oregon — in 2012.

About 67 percent of the new chronic hepatitis C cases reported by the state’s health care providers since 2005 involved a person between ages 40 and 60, according to the Oregon Health Authority’s website.

But these numbers can be misleading, said Thomas and Patty Hutton with the Deschutes County Health Department. Positive tests only come from people who get tested, and up until the task force issued its June statement — which not only encourages boomers to be tested but requires their insurance plans cover these tests as a preventive measure — the only people who got tested fell into one of the disease’s key risk groups or started showing signs of chronic liver disease.

This creates a problem for public health officials because 75 to 80 percent of the people who have a hepatitis C infection are asymptomatic and can pass on the disease without exhibiting its symptoms.

Most people who have a chronic case of hepatitis C — an acute case shows symptoms in less than six months — don’t start getting sick until their 50s and 60s, and that can be decades after they were exposed to the disease and started carrying it around in their systems.

“People start feeling tired or run down,” Hutton said, explaining people sometimes dismiss these symptoms — which are an early stage of kidney disease — as being part of the aging process. “They’ll test positive and have an aha moment where they remember getting a blood transfusion and it clicks.”

Hutton said boomers — who according to the CDC make up about 75 percent of the population with hepatitis C — are at an especially high risk of having the disease because the generation’s men may have received a blood transfusion while serving in the Vietnam War before the blood supply was screened.

“Lots of things were going on then,” she said, adding these returning veterans could have given the disease to a number of other people without even realizing they had it.

There’s very little doctors can do to treat hepatitis C, Hutton said. The best treatment for a chronic hepatitis C infection is to reduce the burden on the liver by not drinking or taking acetaminophen. She said liver transplants are also an option for people who have an extremely severe case of the disease — about 10 to 20 percent of hepatitis C sufferers will develop cirrhosis of the liver, and 1 to 5 percent of them will develop hepatocellular carcinoma (liver cancer) — but transplants only address the symptoms and not the disease.