Tracking Chagas Disease in U.S. States, 2017: Who Reports It and Why

Summary

• An estimated 300,000 people living in the United States have Chagas disease, caused by the parasite Trypanosoma cruzi. Most caught it in countries where it is endemic.
• In 2017, it was reportable in six states. Most cases found — including in blood donors — were chronic infections, not the result of local insect-borne spread.
• Surveillance still matters in states with many travelers from endemic countries or a risk of local spread. It raises awareness among health workers and can link people with chronic infection to treatment.

The disease

As many as 8 million people in Mexico and Central and South America have Chagas disease, and it has become a U.S. concern through immigration from Latin America. It spreads through contact with infected triatomine bugs ("kissing bugs"), from mother to baby, and rarely through organ transplants or blood transfusions. Both the bugs and infected wild animals are found across the United States.

• Acute stage: after a 1–2-week incubation, often no symptoms, or a flu-like illness lasting up to 2 months. Infants are more likely to get severe disease such as myocarditis or meningoencephalitis.
• Chronic stage: untreated, infection becomes lifelong. Most people have no symptoms, but 20%–30% develop heart or digestive complications, which can be fatal.

Limited screening and treatment, and low awareness among health professionals, mean the disease likely has an unrecognized effect on U.S. health care. Prompt diagnosis and treatment can prevent chronic infection.

How the review was done

CDC identified states where Chagas disease is or was reportable, then held telephone interviews with epidemiologists in the six states that tracked it — Arizona, Arkansas, Louisiana, Mississippi, Tennessee and Texas — and in Massachusetts, which once did. They asked why each state made it reportable, who reports cases, what happens next, how the data are used, and whether states track pregnant women at risk, infants of infected mothers, animal infections or the bugs.

What the states do

• Why they started: mainly in response to blood donor screening, and to find out how people were infected.
• Who reports: in five of the six states, blood donor centers, physicians and laboratories; in most, the bulk of reports come from blood centers.
• Investigation: every state investigates to find where exposure most likely happened. Arizona, Louisiana, Mississippi and Texas focus on local transmission; Arkansas and Tennessee collect data on all routes. Four states inspect the patient's home when local exposure is suspected.
• Guidance: with CDC's input, states advise physicians on care. Arkansas sends health alerts to physicians, especially obstetrician-gynecologists caring for pregnant women at risk. No state runs surveillance specifically for congenital infection.
• Sharing data: five states send a report to health care providers, and all six post case counts online or in an annual summary.
• Animals and bugs: no state tracks animal infections systematically. Texas collected reports of infected dogs for 3 years after it began surveillance in 2013, then stopped, finding they did not show human risk. Most states examine insects people send in, forwarding likely kissing bugs to CDC for testing.

Changes over time. Arizona adopted a new case definition in 2016 to classify blood donors using CDC's confirmatory tests. Texas now tracks whether reported cases progress from silent infection to illness, to gauge the burden on health care. Massachusetts made Chagas reportable in 2008, after the FDA approved the first blood donor screening test, to help doctors refer infected donors — but at-risk donors were rarely found, and it dropped the requirement in 2014.

What it means

Local spread is rare. In Latin America, kissing bugs infest poorly built housing and animal hosts live close to people. In the United States, better housing and the lack of transmission involving dogs and people keep the risk of local spread low — and with few acute cases reported, there is little for health departments to respond to.

Babies may be missed. An estimated 63–315 babies are born with T. cruzi infection in the United States each year. Finding and treating them early prevents disease and further spread, but without routine prenatal or newborn screening, congenital cases are hard to catch, and more research is needed on who is at risk and how to screen.

Blood donors are the main window. Awareness rose after donor screening began in 2007; by December 2017, blood banks had reported at least 2,300 infected donors. Screening helps find and treat chronic infections, but understates the true prevalence, because foreign-born Latinos — more likely to be infected — donate blood relatively rarely.

Limitation: the interviews came some time after each state set up surveillance, so answers may suffer from recall bias.

Where resources allow, surveillance is worth doing in states with large at-risk populations — frequent travelers from endemic countries — and where infected animals and kissing bugs create a risk of local spread. It can measure how common the disease really is, raise awareness, reveal unmet care needs, and connect patients to treatment that prevents heart and digestive complications. States with communities at risk might also consider monitoring for congenital infection.

More: CDC's Chagas disease information.

Sources

Based on Carolyne Bennett, Anne Straily, Dirk Haselow and others, "Chagas Disease Surveillance Activities — Seven States, 2017," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.