Rocky Mountain spotted fever epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.

Overview

Incidents of Rocky Mountain Spotted Fever date back to the earlier history of the United States. Since the 1920's the United States Center for Disease Control and Prevention has deemed Rocky Mountain Spotted Fever as a reportable disease. RMSF cases were most often reported within the Rocky Mountain region, although recent data reveals that the disease is widespread throughout the United States.

Epidemiology and Demographics

Incidence

  • 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.
  • CDC compiles the number of cases reported by the state health departments.
  • To ensure standardization of reporting across the country, CDC advises that a consistent case definition be used by all states. [1]
Incidence and case fatality from 1920-2010: Cases of RMSF have been recorded from the 1920s through present day. Trends in RMSF incidence can be observed as ebbs and flows of several years at a time. Periods of increased incidence can be seen between 1930 and 1950 and 1968 through 1990. More recently there has been a more dramatic increase in incidence of RMSF increasing from 1.9 cases per million persons in 2000 to an all-time high of 8.4 cases per million persons in 2008. Case fatality rate was first reported in 1940. Fatality rates vary from year-to-year, but have had an overall decreasing trend from 28% case fatality in 1944 to <1% case fatality beginning in 2001.

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.
  • In Arizona, where transmission is associated with the brown dog tick, peak months of illness onset are August and September.[1]
Proportion of RMSF cases reported to CDC by month of onset, 1993 through 2010: This figure shows the percent of cases reported from 1993 through 2010 by month of onset to give the seasonality of cases. There are cases reported in each month of the year, however most are reported between May and August. Roughly 20% of cases are reported in both June and July.

Geography of Rocky Mountain Spotted Fever

  • RMSF cases have been reported throughout most of the contiguous United States, five states (North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri) account for over 60% of RMSF cases. The primary tick responsible for R. rickettsii in these states is the American dog tick (Dermacentor variabilis Dermacentor andersoni).
  • In eastern Arizona, RMSF cases have recently been identified in an area where the disease had not been previously seen. Through 2009, over 90 cases had been reported, and approximately 10% of the people diagnosed with the disease in this part of the state have died. The tick responsible for transmission of R. rickettii in Arizona is the brown dog tick (Rhipicephalus sanguineus), which is found on dogs and around people’s homes.
  • Almost all of the cases occurred within communities with a large number of free-roaming dogs.[1]
  • Other incidences have recently been reported in portions of California, the Northwest (Washington, and Oregon), and in portions of the Southwest (Arizona, Texas, and New Mexico.)

Age

  • The frequency of reported cases of Rocky Mountain spotted fever is highest among males, American Indians, and people aged 50-69.
  • Individuals with frequent exposure to dogs and who reside near wooded areas or areas with high grass may be at increased risk of infection.
  • Children ages 0-9 and American Indians have an increased risk of fatal outcome from RMSF.[1]
Average annual incidence of Rocky Mountain spotted fever by age-group, 2000 through 2010: This figure shows the average annual incidence of RMSF per million persons by age groups for 2000 through 2010. The graph shows that cases have been reported in every age group with increased incidence as age increases. There is a slightly higher incidence rate in the 5-9 year old age group, which surpasses 4 cases per million persons. The highest incidence rate in observed in age groups 55-59 and 60-64 years old, both of which surpass 8 cases per million persons.

Demographics

  • 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.
  • 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.
  • Infection with Rickettsia rickettsii has also been documented in Argentina, Brazil, Colombia, Costa Rica, Mexico, and Panama. Closely related organisms cause other types of spotted fevers in other parts of the world.

Worldwide Infection

  • 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.
Disease Organism Vector Endemic Regions
Rocky Mountain Spotted Fever [2] Rickettsia Rickettsii Wood Tick (Dermacentor Variabilis), D. andersoni United States:
  • Eastern Region
  • Southwest Region
Helvetica Spotted Fever[3] Rickettsia Helvetica Ixodes Ricinus (European) Europe:
  • Sweden
  • Switzerland
  • France
  • Laos
Ehrlichiosis Anaplasmosis [4] Ehrlichia Chaffeensis, E. Equi Lone Star Tick (Amblyomma Americanum), Ixodes Scapularis United States:
  • South Atlantic Regions
  • South-central Regions
Tularemia [5] Francisella Tularensis D. Andersoni, D. Variabilis United States:
  • Widespread throughout the region, including higher populations in the Southeast, South-central, and the West.
Human neoehrlichiosis [4] [3] Neoehrlichia mikurensis Lone Star Tick (Amblyomma Americanum)' Widespread:
  • Europe
  • Asia
Rickettsiosis [3] Rickettsia No specific species identified Widespread:
  • South Africa
  • Morocco
  • Mediterranean
African tick-bite fever [3] Rickettsia africae Amblyomma, Dermacentor, and Rhipicephalus species Africa:
  • Sub-Saharan
  • West Indies
Queensland tick typhus [6] [3] Rickettsia austalis Ixodes species Widespread:
  • Australia
  • Tasmania
Q-fever (Typhus-like infection) [6] Coxiella burnetii (mimics the mechanisms of Rickettsia) Ixodes holocyclus and Amblyomma triguttatum Australia
  • Widespread throughout Australia
Mediterranean spotted fever (Boutonneuse fever) [7] [3] Rickettsia conorii Brown Dog Tick (Rhipicephalus sanguineus) Widespread:
  • Southern Europe
  • Southern and Western Asia
  • Africa
  • India
Far Eastern spotted fever [3] Rickettsia heilong-jiangensis Tick Widespread:
  • Far portions of Eastern Russia
  • Northern portions of China
  • Eastern Asia
Aneruptive fever [3] [8] Rickettsia helvetica Ixodes species Widespread:
  • Northern and Central portions of Europe
  • Non-specific portions of Asia
Flinders Island spotted fever (Thai tick typhus) [3] [6] Rickettsia honei Tick Widespread in Independent Regions
  • Australia
  • Thailand
Japanese spotted fever [3] Rickettsia japonica Tick Japan
  • Widespread yet isolated to portions of Japan
Mediterranean spotted fever-like disease [3] Rickettsia massiliae and R. monacensis Tick Widespread:

R.massiliae induced:

  • France
  • Greece
  • Spain
  • Portugal
  • Switzerland
  • Sicily
  • Central Africa
  • Mali

R.monacensis induced:

  • Europe
  • North Africa
Maculatum infection Rickettsia parkeri Tick Americas:
  • United States
  • Portions of Canada
  • South America
Tick-borne necrosis and lymphadenopathy [9] Rickettsia raoultii Dermacentor marginatus Widespread:
  • Europe
  • Asia
North Asian Tick Typhus [3] Rickettsia sibirica Tick Widespread:
  • Russia
  • China
  • Mongolia
Lymphangitis [3] Rickettsia sibirica mogolotimonae 'No specific species identified Widespread:
  • Southern France
  • Portugal
  • China
  • Africa
TIBOLA [3] [9] Rickettsia slovaca Dermacentor species Widespread:
  • Southern and Eastern Europe
  • Asia

References

  1. ↑ 1.0 1.1 1.2 1.3 Rocky Mountain Spotted Fever Statistics. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/rmsf/stats/ Accessed on December 30, 2015
  2. ↑ Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015). http://www.cdc.gov/rmsf/ Accessed on December 30, 2015
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 Disease Index General Information, Rickettsia (2015). http://www.cdc.gov/otherspottedfever / Accessed on December 30, 2015
  4. ↑ 4.0 4.1 Disease index General Information (2015). http://www.cdc.gov/parasites/babesiosis/health_professionals/index.html Accessed on December 30, 2015
  5. ↑ Rocky Mountain Spotted Fever Information. Centers for Disease Control and Prevention (2015). \http://www.cdc.gov/tularemia/index.html Accessed on December 30, 2015
  6. ↑ 6.0 6.1 6.2 Australian Tick Index http://www.karlmcmanusfoundation.org.au/ticks-in-oz Accessed on December 30, 2015
  7. ↑ Oztoprak N, Celebi G, Aydemir H, et al. [Mediterranean spotted fever due to contact with dog-tick]. Mikrobiyol Bul. 2008;42(4):7016.http:// http://www.ncbi.nlm.nih.gov/pubmed/19149095 Accessed on December 30, 2015
  8. ↑ Fournier PE, Allombert C, Supputamongkol Y, Caruso G, Brouqui P, Raoult D. Aneruptive fever associated with antibodies to Rickettsia helvetica in Europe and Thailand. J Clin Microbiol. 2004;42(2):816-8. http://http://www.ncbi.nlm.nih.gov/pmc/articles/PMC344501/ Accessed on December 30, 2015
  9. ↑ 9.0 9.1 Dermacentor-borne necrosis erythema and lymphadenopathy: clinical and epidemiological features of a new tick-borne disease. Oteo JA, Ibarra V, Blanco JR, et al. Dermacentor-borne necrosis erythema and lymphadenopathy: clinical and epidemiological features of a new tick-borne disease. Clin Microbiol Infect. 2004;10(4):327-31 http://www.ncbi.nlm.nih.gov/pubmed/15059122 Accessed on December 30, 2015
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