Problem/ConditionDuring 2012–2021, the volume of international travel reached record
highs and lows. This period also was marked by the emergence or large
outbreaks of multiple infectious diseases (e.g., Zika virus, yellow fever,
and COVID-19). Over time, the growing ease and increased frequency of travel
has resulted in the unprecedented global spread of infectious diseases.
Detecting infectious diseases and other diagnoses among travelers can serve
as sentinel surveillance for new or emerging pathogens and provide
information to improve case identification, clinical management, and public
health prevention and response.Reporting Period2012–2021.Description of SystemEstablished in 1995, the GeoSentinel Network (GeoSentinel), a collaboration
between CDC and the International Society of Travel Medicine, is a global,
clinical-care–based surveillance and research network of travel and
tropical medicine sites that monitors infectious diseases and other adverse
health events that affect international travelers. GeoSentinel comprises 71
sites in 29 countries where clinicians diagnose illnesses and collect
demographic, clinical, and travel-related information about diseases and
illnesses acquired during travel using a standardized report form. Data are
collected electronically via a secure CDC database, and daily reports are
generated for assistance in detecting sentinel events (i.e., unusual
patterns or clusters of disease). GeoSentinel sites collaborate to report
disease or population-specific findings through retrospective database
analyses and the collection of supplemental data to fill specific knowledge
gaps. GeoSentinel also serves as a communications network by using internal
notifications, ProMed alerts, and peer-reviewed publications to alert
clinicians and public health professionals about global outbreaks and events
that might affect travelers. This report summarizes data from 20 U.S.
GeoSentinel sites and reports on the detection of three worldwide events
that demonstrate GeoSentinel’s notification capability.ResultsDuring 2012–2021, data were collected by all GeoSentinel sites on
approximately 200,000 patients who had approximately 244,000 confirmed or
probable travel-related diagnoses. Twenty GeoSentinel sites from the United
States contributed records during the 10-year surveillance period,
submitting data on 18,336 patients, of which 17,389 lived in the United
States and were evaluated by a clinician at a U.S. site after travel. Of
those patients, 7,530 (43.3%) were recent migrants to the United States, and
9,859 (56.7%) were returning nonmigrant travelers.Among the recent migrants to the United States, the median age was 28.5 years
(range = <19 years to 93 years); 47.3% were female, and 6.0% were U.S.
citizens. A majority (89.8%) were seen as outpatients, and among 4,672
migrants with information available, 4,148 (88.8%) did not receive pretravel
health information. Of 13,986 diagnoses among migrants, the most frequent
were vitamin D deficiency (20.2%),Blastocystis(10.9%),
and latent tuberculosis (10.3%). Malaria was diagnosed in 54 (<1%)
migrants. Of the 26 migrants diagnosed with malaria for whom pretravel
information was known, 88.5% did not receive pretravel health information.
Before November 16, 2018, patients’ reasons for travel, exposure
country, and exposure region were not linked to an individual diagnosis.
Thus, results of these data from January 1, 2012, to November 15, 2018
(early period), and from November 16, 2018, to December 31, 2021 (later
period), are reported separately. During the early and later periods, the
most frequent regions of exposure were Sub-Saharan Africa (22.7% and 26.2%,
respectively), the Caribbean (21.3% and 8.4%, respectively), Central America
(13.4% and 27.6%, respectively), and South East Asia (13.1% and 16.9%,
respectively). Migrants with diagnosed malaria were most frequently exposed
in Sub-Saharan Africa (89.3% and 100%, respectively).Among nonmigrant travelers returning to the United States, the median age was
37 years (range = <19 years to 96 years); 55.7% were female, 75.3% were
born in the United States, and 89.4% were U.S. citizens. A majority (90.6%)
were seen as outpatients, and of 8,967 nonmigrant travelers with available
information, 5,878 (65.6%) did not receive pretravel health information. Of
11,987 diagnoses, the most frequent were related to the gastrointestinal
system (5,173; 43.2%). The most frequent diagnoses among nonmigrant
travelers were acute diarrhea (16.9%), viral syndrome (4.9%), and irritable
bowel syndrome (4.1%).Malaria was diagnosed in 421 (3.5%) nonmigrant travelers. During the early
(January 1, 2012, to November 15, 2018) and later (November 16, 2018, to
December 31, 2021) periods, the most frequent reasons for travel among
nonmigrant travelers were tourism (44.8% and 53.6%, respectively), travelers
visiting friends and relatives (VFRs) (22.0% and 21.4%, respectively),
business (13.4% and 12.3%, respectively), and missionary or humanitarian aid
(13.1% and 6.2%, respectively). The most frequent regions of exposure for
any diagnosis among nonmigrant travelers during the early and later period
were Central America (19.2% and 17.3%, respectively), Sub-Saharan Africa
(17.7% and 25.5%, respectively), the Caribbean (13.0% and 10.9%,
respectively), and South East Asia (10.4% and 11.2%, respectively).Nonmigrant travelers who had malaria diagnosed were most frequently exposed
in Sub-Saharan Africa (88.6% and 95.9% during the early and later period,
respectively) and VFRs (70.3% and 57.9%, respectively). Among VFRs with
malaria, a majority did not receive pretravel health information (70.2% and
83.3%, respectively) or take malaria chemoprophylaxis (88.3% and 100%,
respectively).InterpretationAmong ill U.S. travelers evaluated at U.S. GeoSentinel sites after travel,
the majority were nonmigrant travelers who most frequently received a
gastrointestinal disease diagnosis, implying that persons from the United
States traveling internationally might be exposed to contaminated food and
water. Migrants most frequently received diagnoses of conditions such as
vitamin D deficiency and latent tuberculosis, which might result from
adverse circumstances before and during migration (e.g., malnutrition and
food insecurity, limited access to adequate sanitation and hygiene, and
crowded housing,). Malaria was diagnosed in both migrants and nonmigrant
travelers, and only a limited number reported taking malaria
chemoprophylaxis, which might be attributed to both barriers to acquiring
pretravel health care (especially for VFRs) and lack of prevention practices
(e.g., insect repellant use) during travel. The number of ill travelers
evaluated by U.S. GeoSentinel sites after travel decreased in 2020 and 2021
compared with previous years because of the COVID-19 pandemic and associated
travel restrictions. GeoSentinel detected limited cases of COVID-19 and did
not detect any sentinel cases early in the pandemic because of the lack of
global diagnostic testing capacity.Public Health ActionThe findings in this report describe the scope of health-related conditions
that migrants and returning nonmigrant travelers to the United States
acquired, illustrating risk for acquiring illnesses during travel. In
addition, certain travelers do not seek pretravel health care, even when
traveling to areas in which high-risk, preventable diseases are endemic.
Health care professionals can aid international travelers by providing
evaluations and destination-specific advice.Health care professionals should both foster trust and enhance pretravel
prevention messaging for VFRs, a group known to have a higher incidence of
serious diseases after travel (e.g., malaria and enteric fever). Health care
professionals should continue to advocate for medical care in underserved
populations (e.g., VFRs and migrants) to prevent disease progression,
reactivation, and potential spread to and within vulnerable populations.
Because both travel and infectious diseases evolve, public health
professionals should explore ways to enhance the detection of emerging
diseases that might not be captured by current surveillance systems that are
not site based.