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Rocky Mountain spotted fever has been a reportable disease in the
United States since the 1920s. In the last 50 years, approximately
250-1200 cases of Rocky Mountain spotted fever have been reported
annually, although it is likely that many more cases go unreported.
Figure 9. Reported cases of Rocky Mountain spotted fever in
the United States, 1942-1996
Seasonal Distribution of Rocky Mountain spotted fever
Over 90% of patients with Rocky Mountain spotted fever are
infected during April through September. This period is the season
for increased numbers of adult and nymphal Dermacentor ticks.
A history of tick bite or exposure to tick-infested habitats is
reported in approximately 60% of all cases of Rocky Mountain spotted
fever.
Figure 10. Seasonal distribution of reported cases of Rocky
Mountain spotted fever, 1993-1996
Geography of Rocky Mountain spotted fever
Over half of Rocky Mountain spotted fever infections are reported
from the south-Atlantic region of the United States (Delaware,
Maryland, Washington D.C., Virginia, West Virginia, North Carolina,
South Carolina, Georgia, and Florida). Infection also occurs in
other parts of the United States, namely the Pacific region
(Washington, Oregon, and California) and west south-central
(Arkansas, Louisiana, Oklahoma, and Texas) region.
The states with the highest incidences of Rocky Mountain spotted
fever are North Carolina and Oklahoma; these two states combined
accounted for 35% of the total number of U.S. cases reported to CDC
during 1993 through 1996. Although Rocky Mountain spotted fever was
first identified in the Rocky Mountain states, less than 3% of the
U.S. cases were reported from that area during the same interval
(1993-1996).
Figure 11. Number of reported cases of Rocky Mountain spotted
fever by state and region, 1994-1998
Persons at Risk for Infection
The frequency of reported cases of Rocky Mountain spotted fever
is highest among males, Caucasians, and children. Two-thirds of the
Rocky Mountain spotted fever cases occur in children under the age
of 15 years, with the peak age being 5 to 9 years old (see Figure
12). Individuals with frequent exposure to dogs and who reside near
wooded areas or areas with high grass may also be at increased risk
of infection.
Figure 12. Average annual incidence of Rocky Mountain spotted
fever by age group, 1993-1996
Worldwide
Infection with Rickettsia rickettsii has also been
documented in Argentina, Brazil, Colombia, Costa Rica, Mexico, and
Panama. Some synonyms for Rocky Mountain spotted fever in other
countries include tick typhus, Tobia fever (Colombia), São Paulo
fever and fiebre maculosa (Brazil), and fiebre manchada (Mexico).
Closely related organisms cause other types of spotted fevers in
other parts of the world (see Table 1).
Table 1. Spotted fever group rickettsiae causing human
disease around the world
|
Organism |
Disease |
Geographic Location |
|
Rickettsia rickettsii |
Rocky
Mountain spotted fever |
North,
Central and South America |
|
Rickettsia conorii |
Mediterranean spotted fever, boutonneuse fever, Israeli
spotted fever, Astrakhan fever |
Europe,
Asia, Africa, Israel, Portugal, Sicily, Russia |
|
Rickettsia akari |
Rickettsialpox |
Worldwide |
|
Rickettsia sibirica (including
"R. mongolotimonae") |
Siberian
tick typhus, North Asian tick typhus |
Siberia,
People's Republic of China, Mongolia, France |
|
Rickettsia australis |
Queensland tick typhus |
Australia |
|
Rickettsia honei |
Flinders
Island spotted fever |
Australia |
|
Rickettsia africae |
African
tick-bite fever |
Africa,
West Indies |
|
Rickettsia japonica |
Japanese
or Oriental spotted fever |
Japan |
|
"Rickettsia
felis" |
no common
name |
United
States, Mexico |
|
Rickettsia slovaca |
no common
name |
Europe |
Other Pages with information on Rocky Mountain Spotted Fever:
Rocky
Mountain Spotted Fever - History
-
Rocky Mountain Spotted Fever Overview
-
Rocky
Mountain Spotted Fever The Organism
-
Rocky Mountain Spotted Fever
Epidemiology
-
Rocky Mountain Spotted Fever
Signs and Symptoms
-
Rocky Mountain spotted fever
Detection
-
Rocky Mountain Spotted Fever
Treatment
-
Rocky Mountain Spotted Fever
Prevention and Control
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