Mediterranean spotted fever--classification by disease course and criteria for determining the disease severity

Mediterranean spotted fever (MSF) in Bulgaria is caused by Ricketsia conorii conorii with a major vector the dog tick, Rhipicephalus sanguineus. The first cases of re-emerging MSF were reported in this country in the early 1990s after some 20 years of absence and then registered an annual increase until 2001-2003 after which the disease prevalence declined. MSF still poses a serious health problem in the country as severe, complicated cases with lethal outcome occur. The aim of this paper was to classify the forms of MSF according to the course of the disease process and to devise criteria for the disease severity in order to enable comparison of clinical manifestations of the disease at different stages of spreading, in different age groups, and between endemic and non-endemic regions in this country and abroad.

The study was carried out in a comparative aspect during the first phase of increase (1993-2003) with incidence of 11.88 per 100000 population and during the second phase of decline (2004-2011) with incidence of 9.56 per 100000 population. The disease was etiologically confirmed in 883 hospitalized patients by the positive antibody response to the specific antigen--Ricketsia conorii conorii by means of the immunofluorescence assay (IFA). The criteria we used for the classification of the forms of MSF included: 1. Typicality: forms having the most characteristic features of the MSF - eschar, fever, papular/maculopapular rash on the trunk and extremities, including hands and feet. 2. Manifestation: forms represented by all or some of the typical symptoms, giving sufficient grounds for preliminary diagnosis. 3.

fulminant, acute and protracted forms. The criteria for severity differentiate between mild, moderate, severe or malignant forms, and include clinical and laboratory parameters as shown in the present study.

Classification of the forms according to MSF course defines them in order of severity, typicality, manifestation, duration of symptoms, complications and age characteristics. According to the accepted criteria for severity and with respect to the studied I and II phase of the disease the mild forms are 41.16%-35.62% (p > 0.05), moderate forms are 32.79%-43.11% (p < 0.01), severe forms are 16.03%-11.37% (p = 0.05), malignant forms are 6.56%-8.68% (p > 0.05), and mortality is 3.46%-1.19% (p < 0.05). The mean age was significantly higher for patients with severe forms of MSF (58.59 +/- 4.32 yrs) compared with those with moderate (46.10 +/- 3.71 yrs, p < 0.05) and mild forms (42.05 +/- 3.50 yrs, p < 0.01). For children up to 14 years old mild forms are more common than in adults over 65 (p < 0.0001). Among children up to 14 years old there were no lethal outcomes, while mortality rate in the patients older than 65 was as much as 10%. All this indicates that MSF runs a milder course in children and a severe, complicated course in the elderly.

The criteria for MSF severity we have selected are based on our own experience and the experience of other authors. They are based on the reaction of human organism to the pathogenic agent and can be used during the different phases of emergence and development of rikettsial diseases, regardless of their geographic distribution. Unified use of these criteria would eliminate the differences in the data reported by different researchers regarding the disease development and severity.