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Chikungunya epidemiology in U.S. territories and
states with risk of transmissionNational Center for Emerging and Zoonotic Infectious Diseases
Susan Hills MBBS MTH
CDC Lead , Chikungunya Vaccines Work Group
Arboviral Diseases Branch
Division of Vector- Borne Diseases
Fort Collins, Colorado
ACIP Meeting, June 26, 2024
•Mosquito -borne disease
•Key vectors are Aedes aegypti
and Aedes albopictus mosquitoesChikungunya
•Typically tropical and subtropical
regions
•Periodically causes large outbreaks
-Often high attack rates
•Virus transmission usually highest
during wet seasonDistribution and disease burden in endemic areas
Countries and territories with current or past
transmission of chikungunya virus
•Febrile illness with typically severe
a
rthralgia, can be debilitating
•Other symptoms include headache,
r
ash, myalgia, anorexia
•No anti - viral treatment availableClinical features of acute chikungunya virus infection
•Rare serious complications (e.g.,
myocarditis, hepatitis, neurologic illness)
•Deaths rare and reported mostly in
-Older adults, particularly those with comorbidities
-Young infants infected perinatally or by mosquito bitesComplications of chikungunya
Images from : https://www.paho.org/en/topics/chikungunya
•Acute symptoms usually resolve in 7 –10 days
•Some patients have continuation or relapse
of symptoms
•Ongoing arthralgia of variable severity possibly present in up to ~50% at 3 months and ~30% at 12 monthsChronic arthralgia following chikungunya
Puerto Rico
•Largest U.S territory
-Po pulation ~3.2 million persons
-Area ~3,500 miles2
•Tropical climate
•Aedes aegypti pr esent
•Dengue endemic Puerto Rico
•Data from passive and sentinel surveillance systems
•No single data source provides accurate and complete information
•Surveillance activities, reporting practices, and laboratory testing
approaches changed during outbreak
-When laboratory capacity exceeded, testing prioritized for certain groups
-When number of suspected cases reached thousands per week, limitation on
types of cases to be reported
•Key points
-Numbers of cases often substantial underestimate of true cases
-Data provide reasonable representation of actual disease epidemiologyData sources
•Confirmed cases : detection of nucleic acid by RT -PCR
•Probable cases : IgM antibodies in serum or cerebrospinal fluid
•Chikungunya IgM antibodies can persist after acute infection
•13–18 months: 56% with IgM1
•2–3 years: 11% with IgM2 Laboratory criteria for chikungunya cases
1. Grivard et al, Path Biol 2007; 2. Costa et al, Rev Soc Bras Med Trop 2021
•Chikungunya emerged in 2013
-First case reported in Saint Martin island in December
•Rapid increase in countries and territories reporting transmission
•In Puerto Rico, first laboratory -confirmed case in May 2014Chikungunya emergence in the Caribbean
Chikungunya cases reported by year and case status,
Puerto Rico, 2014 –2020
0200040006000800010000
2014 2015 2016 2017 2018 2019 2020Probable
Confirmed
Chikungunya cases reported by year and case status,
Puerto Rico, 2014 –2020
0200040006000800010000
2014 2015 2016 2017 2018 2019 2020Probable
Confirmed
Last laboratory -confirmed
symptomatic clinical case
Chikungunya cases by month of illness onset during
two main outbreak years, 2014 –2015
050010001500200025003000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2015 2014
Chikungunya cases by sex, Puerto Rico, 2014 –2020
(N=10,293)*
Sex No. (%)
Female 5,116 (52%)
Male 4,708 (48%)
*n=469 with unknown sex
Chikungunya cases by age group, Puerto Rico, 2014 –
2020 (N=10,293)*
Years No. (%)
0–19 4,328 (42%)
20–39 2,055 (20%)
40–59 1,931 (19%)
≥60 1,865 (18%)
*n=114 with unknown age
Chikungunya cases by municipality, Puerto Rico,
2014 –2020
•Household cluster survey among persons aged 1– 50 years in one
municipality in southern Puerto Rico in 2018– 2019
-31% seroprevalence1
•Samples from blood donors aged ≥16 years collected in March 20152
-23% seroprevalence2
•Based on 30% seroprevalence rate, ~ 1 million persons estimated to have
been infected during outbreak
-~650,000 –85 0,000 clinical cases Proportion of Puerto Rico population infected
1. 1,268 of 4,035 participants (Adams LE at al, PLoS NTD 2022); 2. 242 of 1,031 samples (Simmons G et al, Emerg Infect Dis 2016)
United States Virgin Islands (USVI)
•First locally acquired case detected in
early June 20141
•Initial transmission on Saint ThomasInitial transmission of chikungunya in USVI
Source: https://ontheworldmap.com/virgin -islands- us/
1. Feldstein LR et al, Am J Trop Med Hyg 2016
Epidemic curve of chikungunya cases* by island, USVI,
2014 –2015 (N=637)
*Confirmed or probable Feldstein LR et al, Am J Trop Med Hyg 2016
Last laboratory -
positive case
February 2015
•31% persons had evidence of past infection in seroprevalence survey
approximately 1 -year post -outbreak1
•~33,000 persons estimated to have been infected during outbreak
-~21,000– 28,000 clinical cases during 8- month outbreak periodProportion of USVI population infected, 2014 –2015
1. Hennessey MJ e al, Am J Trop Med Hyg 2018 *Laboratory confirmed or probable
Other U.S. territories and freely associated states
•American Samoa1
-Outbreak began June 2014
-Unconfirmed information suggested ≥823 suspected cases
-Unclear duration but no evidence of transmission by end of 2015
•Guam and Commonwealth of the Northern Mariana Islands (CNMI)
-No cases reportedOther U.S. territories
1. Roth A et al, Eurosurveillance 2014; ArboNET data
•Federated States of Micronesia (Yap State)1
-Outbreak from Aug 2013 –Aug 2014 with peak Oct –Dec 2013
-1,761 suspected cases reported
-Attack rate of 155 clinical cases per 1,000 population, so ~15% population sought
care for suspected illness
•Marshall Islands2
-Outbreak began February 2015
-Unclear duration and extent but unconfirmed information suggests >1,000
suspected cases
•Palau
-No cases reportedFreely associated states
1. Pastula DM et al, PLoS NTD 2017; 2. Ministry of Health Republic of the Marshall Islands Chikungunya Report, April 2015.
•3 territories and 2 affiliated states have had chikungunya outbreaks
•Outbreaks were explosive
•For Puerto Rico and USVI, ~30% of population was likely infected, with
20% –25% of the population having clinical illness mainly during a period ~6
months
•All outbreaks began 2013– 2015
•No evidence of confirmed transmission since 2017 (Puerto Rico) or earlier
in islands with smaller populations
•Timing of future transmission or outbreaks and likely pattern unknown Summary:
Chikungunya in U.S territories and affiliated states
Locally -acquired cases in U.S states
Aedes aegypti Aedes albopictus Estimated potential range of Aedes aegypti and Aedes
albopictus in the United States, 2017
https://www.cdc.gov/mosquitoes/php/toolkit/potential -range -of-aedes.html
•First local transmission of chikungunya virus in
c
ontinental United States was in 2014
•Occurred in context of chikungunya outbreak in
Ame
ricas and increase in traveler cases
•After 1st locally -acquired case in June, 11 additional
cases identified in 4 counties in southern Florida
•Two patients lived within 1,500 feet of each other and
o
ther cases were sporadic reportsFlorida (N=12)*#
*11 cases described in MMWR and one case reported after MMWR published
#Does not include one case from different area of Florida published by clinician in 2021 (Am J Emerg
Med, 2021) as IgM positive result not confirmed when tested by neutralizing antibody testing
Kendrick K, et al. MMWR 2014;63(48):1137
Texas (N=1)
•One case in Cameron County
•Occurred in November 2015
Mexico
Location of Cameron County, Texas
For more information, contact CDC
1-800- CDC- INFO (232 -4636)
TTY: 1 -888- 232- 6348 www.cdc.gov
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Acknowledgments
•Puerto R ico Department of Health
•Nicole Lindsey, Arboviral Diseases Branch
•Laura Adams, Dengue Branch
•Joshua Wong, Dengue Branch