1 figure omitted
The majority of malaria cases diagnosed in the United States are imported,
usually by persons who travel to countries where malaria is endemic.1 However, small outbreaks of locally acquired mosquito-transmitted
malaria continue to occur.2 Despite certification of malaria eradication
in the United States in 1970,3,4 11 outbreaks involving 20 cases
of probable locally acquired mosquito-transmitted malaria have been reported
to CDC since 1992,5-7 including two reported in July 1996 from
Palm Beach County, Florida (Palm Beach County Health Department, unpublished
data, 1998). This report describes the investigation of seven cases of locally
acquired Plasmodium vivax malaria that occurred in
Palm Beach County during July-August 2003. In addition to considering malaria
in the differential diagnosis for febrile patients with a history of travel
to malarious areas, health-care providers also should consider malaria as
a possible cause of fever among patients who have not traveled but are experiencing
alternating fevers, rigors, and sweats with no obvious cause.
Case 1. On July 24, a man aged 37 years was
admitted to hospital A with a 6-day history of fever, chills, headache, anorexia,
and vomiting. On July 25, P. vivax was identified
on a blood smear. The patient recovered after treatment with doxycycline,
quinine, and primaquine. The patient is a plumber who reported working outside
during the day but who stayed indoors at night.
Case 2. On July 22, a man aged 46 years reported
to the emergency department (ED) of hospital A with a 3-day history of fever,
headache, chills, anorexia, nausea, vomiting, dehydration, and malaise. He
was treated with intravenous fluids and discharged with levofloxacin. On July
24, he returned to the ED with worsening symptoms and was admitted with a
diagnosis of pneumonia. On July 25, P. vivax was
identified on a blood smear. The patient recovered after treatment with doxycycline,
quinine, and primaquine. The patient is a construction worker who reported
Case 3. On August 15, a man aged 32 years was
admitted to hospital A with a 33-day history of fever, chills, headache, vomiting,
and intermittent sweating. He had consulted several physicians for his symptoms
and had been treated unsuccessfully with azithromycin and prednisone. On the
day of admission, P. vivax was identified on a blood
smear. The patient recovered after treatment with doxycycline, quinine, and
primaquine. He reported having played golf and tennis in the evenings.
Case 4. On August 19, a man aged 45 years visited
the ED of hospital A with a 2-day history of fever, chills, anorexia, arthralgias,
and diarrhea and was discharged on ibuprofen. The patient visited the ED again
on August 21 for these same symptoms, was evaluated, and discharged. On August
22, he returned to the ED with worsening symptoms and mental confusion and
was admitted; a blood smear demonstrated the presence of P. vivax. He recovered after treatment with chloroquine and primaquine.
The patient slept in a homeless camp in a wooded area near a canal. He reported
using insect repellent.
Case 5. On August 24, a man aged 23 years was
admitted to hospital A with a 12-day history of fever, chills, arthralgias,
diarrhea, and vomiting. On the day of admission, P. vivax was identified on a blood smear. He had visited the ED several days
previously with the same complaints and had been treated with antibiotics
for a respiratory infection. The patient recovered after treatment with chloroquine
and primaquine. He reported fishing at a community pond in the evenings.
Case 6. On August 25, a person aged 17 years
was admitted to hospital B with an 8-day history of fever, chills, and headaches.
On August 26, P. vivax was identified on a blood
smear. He recovered after treatment with doxycycline, quinine, and primaquine.
The patient is a student and reported spending time at a pond near his house.
Case 7. On August 26, a man aged 48 years was
admitted to hospital C with a 7-day history of fever and chills. He had self-treated
earlier that week with antibiotics. P. vivax was
identified on a peripheral blood smear on the day of admission. He recovered
after treatment with chloroquine and primaquine. The patient is a carpenter
and works until 8 p.m. in an open warehouse.
All seven patients reported having no previous history of malaria, recent
blood transfusion, organ transplantation, or intravenous drug use. Six of
the seven patients reported never having traveled to regions where malaria
is endemic. Patient 7 emigrated to the United States from Bogota, Colombia,
in July 2001; although Bogota is free of malaria transmission, malaria is
endemic in some areas of Colombia.
All seven patients live within the West Palm Beach area within 10 miles
of Palm Beach International Airport. No international seaport exists nearby.
Patients 1 and 2 attended the same local party on July 4. None of the other
patients had any known common activities or interactions.
Blood specimens were reviewed, and P. vivax infection
was confirmed by both microscopic diagnosis and polymerase chain reaction
rRNA gene analysis. In addition, parasite multilocus genotyping confirmed
that all seven patients were infected by the same strain of P. vivax.
Targeted mosquito trapping was conducted within 1 mile of the homes
of patients. Anopheles quadrimaculatus (n = 33) and An. crucians (n = 425) were tested by CDC. None demonstrated
the presence of malaria parasites.
Several strategies to prevent further transmission of malaria and to
enhance case detection were implemented by the Palm Beach County Health Department.
Reverse 911 telephone calls delivering a prerecorded message, warning of the
presence of malaria in the region and advising the use of prevention measures,
were made to all homes in the county; approximately 300,000 residents were
reached. Postcards in multiple languages were mailed to residents. Flyers
and posters in English and Spanish were distributed at soup kitchens, trailer
parks, and at outdoor activities at which persons were at high risk for malaria.
Local media were encouraged to provide relevant malaria messages in multiple
languages. Multilingual notices were sent home with all public school students.
Several local homeless camps were visited to distribute brochures and
insect repellent. Case-finding was conducted after reports of fever in these
camps. One person was evaluated for malaria, but his smears did not demonstrate
the presence of malaria parasites.
Notices were sent to local physicians and hospitals by e-mail, fax,
and mail, informing them of the presence of malaria and requesting information
and advising testing for persons with a history of unexplained fever.
Mosquito-control practices were already in place in Palm Beach County
for control of the West Nile virus vector and nuisance mosquitoes. Additional
mosquito spraying was implemented within a 3-mile radius of the homes of each
JM Malecki, MD, S Kumar, MD, BF Johnson, ML Gidley, TE O'Connor, J Petenbrink,
Palm Beach County Health Dept; L Bush, MD, J Morand, MT Perez, MD, JFK Hospital,
Palm Beach County; S Pillai, PhD, L Crockett, MD, C Blackmore, DVM, Florida
State Health Dept; E Bradford, Palm Beach County Mosquito Control, Florida.
RA Wirtz, PhD, JW Barnwell, PhD, AJ DaSilva, PhD, LM Causer, MBBS, ME Parise,
MD, Div of Parasitic Diseases, National Center for Infectious Diseases, CDC.
This outbreak shares common features with other outbreaks of malaria
reported previously in the United States, including (1) an initial introduced
case without risk factors for malaria, (2) presence of competent malaria vectors,
(3) proximity to a person with malaria parasitemia, and (4) environmental
conditions conducive to the maturation of the parasite in the mosquito. Possible
infected persons providing a source for this outbreak in Palm Beach County
include both international travelers and the immigrant population, including
migrant farm laborers from Mexico and Central and South America.
This outbreak represents the first reported outbreak of malaria with
extended transmission in the United States since 1986.8,9 Early
cases might have been sources of subsequent cases or ongoing transmission
might have resulted from an index patient with unresolved parasitemia being
the source for each subsequent case. Also unique to this outbreak has been
the use of molecular techniques to genetically type the strain of the infecting
parasite. These results support the hypothesis that this cluster of cases
was the result of extended malaria transmission originating from a single
This outbreak demonstrates the potential for reintroduction of malaria
into the United States despite intensive surveillance, vector-control activities,
and local public health response to educate clinicians and the community.
Rapid recognition, accurate diagnosis, and appropriate case management are
essential for limiting the spread of a malaria outbreak. If an outbreak has
occurred, clinicians must consider malaria in the diagnosis of any patient
with fever without apparent cause. Prevention of mosquito bites through personal
protection measures (e.g., using insect repellent containing DEET) and vector
control are important measures to limit transmission. Risks for locally acquired
malaria are unlikely to abate given migration and travel patterns and a global
yearly malaria burden of 300-500 million cases and one million deaths. However,
prompt reporting of patients with malaria to public health authorities and
adequate assessment of risk factors for malaria in all cases allows initiation
of an appropriate public health response to prevent reestablishment of malaria
References: 9 available
Local Transmission of. JAMA. 2003;290(22):2931-2934. doi:10.1001/jama.290.22.2931