(CNN) - Tennessee is the most recent state to report an outbreak of hepatitis A, with Nashville claiming 14 confirmed cases since December.
Hepatitis A is a viral infection that causes inflammation of the liver. Over the past two years, six other states have experienced outbreaks, and although demand for the vaccine outpaced supply earlier this year, there is enough supply to satisfy current needs, according to the US Centers for Disease Control and Prevention.
California, Indiana, Kentucky, Michigan, Utah and West Virginia have reported outbreaks of hepatitis A since March 2017. Cases in these states, with the exception of Michigan, have been genetically identical or similar, according to the CDC. Laboratory reports have not determined whether the viral strains from cases in Nashville are also genetically linked.
Symptoms of hepatitis A, which include fever, fatigue, nausea, abdominal pain and jaundice (yellowing of the skin and whites of the eyes), usually last less than two months, although some people can be ill for as long as six months, according to the CDC.
Most patients recover completely and do not have any lasting liver damage.
Hepatitis A is typically spread when people eat contaminated food or water; more rarely, the virus is transmitted person-to-person through poor hygiene and close contact. Although there are no special treatments, doctors recommend rest, adequate nutrition and fluids.
Generally, people get sick between 15 and 50 days after their first exposure to the virus. Infected people can spread the virus one to two weeks before their own symptoms appear and up to one week after they develop jaundice, usually a late-appearing symptom.
Vaccination is the best way to prevent an infection, according to the CDC, which has worked with public health officials in affected areas to provide guidance about targeting the vaccine to at-risk populations and has collaborated with manufacturers to increase the national supply.
"The supply for children is fine, and there is enough adult supply to meet demand," CDC spokeswoman Kristen Nordlund said. "As for people talking to their doctors, it would depend on whether their doctor stocks the vaccine."
She added that the CDC does not have a preferential recommendation among the hepatitis A vaccines licensed by the Food and Drug Administration, which include Havrix and Twinrix, both produced by GlaxoSmithKline, and Vaqta, produced by Merck.
CDC and vaccine manufacturers continue to monitor ongoing demand for hepatitis A vaccine closely, Nordlund said.
Due to the outbreak, the CDC recommends hepatitis A vaccination for people who are homeless and who use drugs, the two populations most at risk for becoming infected.
Generally, inoculation with the vaccine is recommended for all children at age 1; men who have sex with other men; users of recreational drugs; people with chronic or long-term liver disease; people with clotting-factor disorders; people with direct contact with people infected with hepatitis A; travelers to countries where hepatitis A is common and family and caregivers of adoptees from those countries; and anyone else who wants protection against the disease.
California was the first state to announce an outbreak in 2017, saying it began in November 2016. The state reported a demobilization of response as of April 11, though state, county and local health authorities continue to monitor the situation.
As of April 11, California reported 704 cases, 461 hospitalizations and 21 deaths. The majority of cases -- 587 -- occurred in San Diego, though Santa Cruz, Los Angeles, Monterey and other counties were also affected. Subsequent hepatitis A cases will be included in the state's annual surveillance reports.
"The majority of people who have been infected with hepatitis A virus in this outbreak are people experiencing homelessness and/or using illicit drugs in settings of limited sanitation," according to the California Department of Public Health website. "Other states are experiencing outbreaks in similar populations of at-risk people."
Since November, the Indiana State Department of Health has identified an increase of hepatitis A cases in the southern part of the state, with most patients residing in Clark and Floyd Counties.
The state reported a total of 107 hepatitis A outbreak-related cases as of May 25, with 51 hospitalizations. Many of the infected people have an association with patients in the large outbreak in neighboring Kentucky, according to the health department's website, which also notes that, generally, the state averages just 20 cases of hepatitis A per year.
In November, the Kentucky Department for Public Health identified an outbreak of hepatitis A. The state reported 629 total cases, 401 hospitalizations and six deaths as of May 21.
"Similar to hepatitis A outbreaks in other states, the primary risk factors have been homelessness and illicit drug use," the health department noted.
"It's a rare disease," said Dr. Jeffrey Howard, acting commissioner of the Department of Public Health, in a presentation recorded on Facebook. The state normally reports 20 cases annually, he added.
"This outbreak is occurring across the country," Howard said, adding that it is believed the outbreak started in San Diego and then spread from there. "I suspect many, many states across the country will declare an outbreak, and they will see a rising number of cases."
Michigan has been dealing with an outbreak of hepatitis A since August 2016, with 837 total cases as of May 23, including 671 hospitalizations and 27 deaths. Most of the illness has occurred in Macomb, Wayne and Oakland counties as well as in the city of Detroit.
The state reported that it is continuing to see an elevated number of hepatitis A cases as of May 23.
Though the confirmed number of Nashville patients since December is only in the mid-teens, "national experts at CDC are involved and providing laboratory testing and technical consultation and support as needed," said Brian Todd, a spokesman for Music City's Metro Public Health Department. "Part of the overall effort is to try to identify the source of the outbreak; however, it is too early to make that determination."
According to Todd, the Metro Public Health Department had a supply of vaccine on hand and received an additional 1,000 doses from the Tennessee Department of Health on Thursday.
"We still have a good supply of vaccine, and additional vaccine is available as needed," he said.
Based on confirmed cases, the city's immediate priority for vaccination includes men who have sexual contact with men and illicit drug users, Todd added. "We are considering those experiencing homelessness as an at-risk group even though there have been no cases," he said. "We have typically seen an average of two cases each year in Nashville over the past few years."
Utah, which identified its own outbreak of hepatitis A beginning in January 2017, reported 266 confirmed cases related to the outbreak as of Tuesday. Salt Lake County, which has reported 148 total cases including two deaths as of April 2, has carried most of this burden.
"In response to the outbreak, public health officials have been working to identify cases and contacts, provide education, and ensure opportunities for vaccination of close contacts to cases and vulnerable populations," according to state health authorities.
West Virginia reported 106 cases of hepatitis A as of May 23. Kanawha and Putnam counties have experienced most of these cases. In response to the outbreak, the state health department is providing hepatitis A vaccination clinics for restaurant and food service employees in those two counties, since at least one worker in eight food establishments have confirmed infections.
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