in israel , all cases of tbrf in civilians are reported to the ministry of health and investigated by an epidemiologist nurse . cases in soldiers are reported to the military health branch of the surgeon general headquarters of the israel defense force . we evaluated the demographic , clinical , and geographic data from reports of civilians from 1971 to 2003 and of soldiers from 1975 to 2003 . we included confirmed cases , in which a person had both febrile illness and a positive peripheral blood smear , and associated cases , in which a person had a relapsing febrile illness and was associated with a confirmed case . tests for trends were conducted with pepi software , version 4.0 ( sagebrush press , salt lake city , ut , usa ) . a total of 606 cases were reported during the study years , 283 in civilians , and 323 in soldiers . the yearly incidence average in civilians declined from 0.35 cases per 100,000 population from 1975 to 1985 to 0.11 cases per 100,000 population from 1986 to 2003 ( p<0.001 ) . the peak in civilian cases in 1984 and 1985 was unexplained ; 2 cases occurred in immigrants from ethiopia 3 months after they arrived in israel . the incidence of tbrf in the military from 1983 to 2003 has been relatively constant , with an average of 6.4 cases per 100,000 population annually ( figure 1b ) . of 359 patients for whom this information was available , 304 ( 85% ) were of jewish origin and 55 ( 15% ) were of non - jewish origin , similar to the proportions in the israeli population . the most commonly reported exposures were visiting caves ( 64% ) , visiting abandoned buildings ( 5% ) , and engaging in other outdoor activity ( 19% ) . in 12% of the cases , exposure to caves was excluded , but the exposure circumstances were not identified . in soldiers , 43% of cases were associated with outdoor exposure , usually related to prolonged periods of lying on the ground . in civilians , 49% were students and 16% were outdoor workers . one hundred cases occurred in clusters with an average of 3.3 ( range 210 ) people in each cluster . soldiers comprised more than half of the total cases in this study , with an average incidence 36 times greater than in civilians . the higher incidence in soldiers may be due to increased risk of exposure because of their specific activities or better case reporting in the israel defense force . during the last century in industrialized countries , this decline can be attributed to elimination or significant reduction of pathogens or decreased exposure to the pathogens . this study has shown a decrease in the incidence of tbrf in civilians , with no similar decrease in soldiers . this decrease becomes even more evident when compared to the incidence in israel during the 1950s and 1960s ( figure 2 ) . that the incidence has remained similar over time among military personnel indicates that the pathogen and the vector continue to exist in israel and that soldiers are at a high risk of contracting it because of their activities . infection has occurred although israel defense force commanders are aware of tbrf and all soldiers and commanders receive annual guidelines on preventing tbrf . furthermore , entering caves is prohibited , and most tbrf cases in the military ( 67% ) were not due to cave exposure . the declining incidence among civilians is likely due to a decrease in the rate of exposure with increased urbanization . a civilian subpopulation that continues to be at risk although tbrf was reported throughout the year , most cases occurred during summer and fall . possible explanations include higher ornithodoros tick activity , higher human outdoor activity , and lighter clothes worn during these seasons . tbrf can be contracted throughout israel , despite the varying climatic conditions ( table ) . in soldiers , 63% of cases were contracted in the hot , arid , southern regions of israel . the high number of cases in the southern regions is probably because most military training activity is conducted there . in civilians , more cases were contracted in the northern and central regions of israel where more persons travel . that 64% of the cases are associated with caves might be explained by the relatively stable conditions in caves that are favorable to ticks . although women also served in the israeli military , only a fraction of them served in positions that required outdoor exposure . this tendency has been observed in previous reports , and likely results from men s high - risk behavior . in conclusion , tbrf continues to be endemic in israel and still poses a considerable hazard for soldiers and civilians . although tbrf has been substantially reduced in civilians , the incidence in soldiers has not declined . sufficient information on the habits of the o. tholozani tick and its reservoirs is not available . to reduce the incidence of tbrf further studies are also needed to identify borrelia reservoirs in israel and to study the habits of its vector .
we evaluated the epidemiology of relapsing fever from 1971 to 2003 in israel . in civilians , 
 incidence declined from 0.35 to 0.11 cases per 100,000 persons annually ; in military personnel it averaged 6.4 cases per 100,000 persons annually . 
 these data imply that the pathogen and vector continue to exist in israel .