Wind in November, Q fever in December

Emerging Infectious Diseases, July, 2004 by Herve Tissot-Dupont, Marie-Antoinette Amadei, Meyer Nezri, Didier Raoult

Q fever, a worldwide zoonosis caused by Coxiella burnetii, can be transmitted from animal reservoirs to humans by the inhalation of infected aerosols. We investigated the epidemiology of Q fever in the Bouches-du-Rhone district of southern France, particularly the role of wind and rainfall in C. burnetii transmission. During the winter of 1998 to 1999, an unexpected number of cases were diagnosed in the area. This statistically higher incidence was associated with an increased frequency of the mistral 1 month before onset of disease, i.e., shortly after the main lambing season. These data confirm that wind plays a role in C. burnetii transmission, a factor that can be monitored but not prevented. Further studies are needed to identify and confirm preventable individual behavioral risk factors for Q fever.

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Q fever is a worldwide zoonosis caused by Coxiella burnetii, an obligate intracellular bacteria which lives the phagolysosomes of the host cell. The main characteristic of Q fever is its clinical polymorphism. Acute cases, which are symptomatic in less than 50%, generally manifest as an insolated fever or a flulike syndrome that may be accompanied by granulomatous hepatitis, pneumonia, or meningoencephalitis (1). Cases with febrile eruptions, myocarditis, and pericarditis have also been reported (2); the various clinical manifestations may depend on host factors (2). In chronic Q lever, endocarditis is the primary sign (3), although osteomyelitis, infections of vascular grafts or aneurisms (4), and pregnancy complications (5) have also been reported. Thus, a serologic confirmation is required for the diagnosis of Q fever.

Throughout the world, the most common reservoirs of C. burnetii are cattle, sheep, and goats (6); the bacterium is found in urine, feces, milk, and birth products of infected animals (7). Also, infected cats (8), rabbits (9), and dogs (10) can transmit C. burnetii to people. Human infections mainly occur after persons inhale contaminated aerosols and, rarely, after they ingest unpasteurized milk or cheese.

The role of wind in aerosol transmission has been suggested since the 1950s (11). Two large outbreaks of Q fever have been studied extensively and have provided additional information about the disease's epidemiology. In a British study (12), Q fever developed in persons who were exposed to contaminated straw, manure, and dust introduced by the vehicles that traveled along the road where these persons lived. In a Swiss study (13), Q fever also developed in 415 persons who lived on a valley road along which sheep were herded to mountain pastures. Table 1 summarizes the other main outbreaks reported over the last 20 years.

In a survey carried out from 1995 to 1997 (28), the study area (40 km northwest of Marseille) was shown to have an incidence of Q fever 5.4 times higher than that of the area of Marseille. This hyperendemicity could be due to wind blowing through an extensive sheep-rearing area before reaching the study area. The main peak of Q fever cases occurs in April and May in the disease-hyperendemic area, 1 month after the second lambing season, which takes place when the strongest winds blow. At the time of the main lambing, in October and November, the wind is infrequent, leading to a small number of Q fever cases.

During the winter of 1998 to 1999, an unexpected number of cases were diagnosed in this area. Our study attempted to confirm our previous hypotheses by correlating this unusual winter peak of infections with unusual meteorologic events.

Materials and Methods

Serologic Diagnosis

The serologic diagnosis of Q fever was performed at the National Reference Center by using the immunofluorescence reference technique as previously described (29). The titers of immunoglobulin (Ig) G, IgM, and IgA against phases I and II of C. burnetii were determined. A case of evolving Q fever (acute or chronic) was diagnosed when the phase II IgG titer was [greater than or equal to] 200 and the phase II IgM titer was [greater than or equal to] 50. A diagnosis of chronic Q fever was made when the phase I IgG titer was [greater than or equal to] 800 (29).

Demographic, Geographic, and Meteorologic Data

Marseille is a city located in southern France with 1 million inhabitants. About 40 km northwest of Marseille is a large, natural, saltwater lake called "Etang de Berre" (Figure 1). Northwest of Etang de Berre is a 600-[km.sup.2], semidesert plain region called "La Crau," which is the only steppe in Western Europe. La Crau is limited by the Alpilles Mountains (north), the Mediterranean Sea (south), the Etang de Berre (west), and the Rhone River (east). The irrigated northern area (humid Crau) is devoted to hay cultivation (120 [km.sup.2]), whereas the stony and dry southern part is devoted to sheep grazing.

[FIGURE 1 OMITTED]

Data on sheep breeding were obtained from the "Chambre d'Agriculture" in Aix en Provence. These data included the approximate number of sheep and the features of sheep breeding in the area.