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108 cases of Q Fever among visitors to a cave in Spain

Spain experienced a significant outbreak of Q Fever, involving a total of 108 cases, out of which 53 presented pneumonia, and 27 necessitated hospitalization. 

The outbreak initiated in February 2021 among rock climbers who were exploring a cave in Biskay, in the north of Spain, and concluded in October 2021. Q Fever, caused by Coxiella burnetii, is a zoonotic disease with ruminants as common carriers. Humans inhale aerosols contaminated with C. burnetii from infected animals, resulting in various clinical manifestations. 

Goats sheltering in the cave were identified as the likely source of infection, leading to cave closure, animal movement restrictions, and vaccination

This Q Fever outbreak underscores the necessity of a multidisciplinary One Health approach, as it emerged unexpectedly in a natural setting with animal presence.

Disease detection in Q Fever outbreak

The limestone cave of Biskay in the Basque Country of Spain is frequently visited by tourists and rock climbers. Bats inhabit the lateral gallery, while local farms maintain goats and sheep, with some animals having access to the cave’s outer sections.

A thorough epidemiological investigation was led by the Basque Epidemiological Surveillance Unit. Suspected cases were provided with questionnaires to collect information on personal details, cave visits, livestock interactions, protective measures, and symptoms to find possible ways of transmission or contamination. Pairs of blood samples were obtained from suspected cases, and serological analyses utilizing an immunofluorescence antibody test were conducted across various healthcare facilities.  

The majority of cases emerged after the Easter holiday in April-May 2021, disproportionately affecting more males (63.9%) than females (36.1%), with median ages of 42 and 39 years, respectively. The causative agent, Coxiella burnetii, responsible for Q Fever, was detected using PCR analysis in samples collected from within the cave, including fecal matter, dust, and aerosols, spanning from March 2021 to February 2023.

Cases were classified as confirmed if they displayed fitting clinical symptoms (fever, pneumonia, and/or hepatitis) between December 2020 and October 2021, along with positive phase II IgG or IgM antibody outcomes or seroconversion within 40 days post-visit. Probable cases encompassed individuals with akin symptoms but lacked laboratory confirmation or demonstrated milder respiratory symptoms with positive IgM results.

Possible causes and discussions about the Q Fever outbreak

According to the questionnaire, despite the prevailing COVID-19 pandemic guidelines advocating the use of facial masks, merely half of the impacted visitors acknowledged wearing masks. Approximately one-third of them admitted to sporadic mask usage during their time in the cave. The cave’s popularity during the Easter holidays attracted many local visitors who perceived it as an open environment, leading them to disregard face mask recommendations, even outdoors, and consequently increasing their exposure to Coxiella burnetii. 

Notably, pneumonia, the prevalent clinical manifestation of Q Fever symptoms in northern Spain, was also the predominant presentation during this outbreak. Q Fever diagnosis delays arose due to initial testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) upon hospitalization, which hindered the timely confirmation of Q Fever cases. 

Moreover, patients with respiratory symptoms who tested positive for SARS-CoV-2 were not further investigated for Q Fever. Given these factors, the reported Q Fever case count might have underestimated the true extent of the outbreak.


This outbreak showcases the unexpected occurrence of Q Fever in natural environments and highlights the importance of comprehensive approaches for outbreak management, especially when zoonotic pathogens are involved.

Zoonotic diseases can arise not solely from direct interactions with animals but also from environmental sources. To effectively manage such outbreaks, it is crucial to adhere to guidance provided by public health specialists, and individuals involved in cleaning and disinfection should employ personal protective gear. Lowering the occurrence of Coxiella burnetii in ruminants will result in a decreased likelihood of outbreaks.

The all-encompassing One Health approach spanning multiple sectors and the implementation of public health strategies have proven successful in managing this Q Fever outbreak, with no new human cases reported since October 2021.

Restricting access to the cave for goats and sheep, combined with rigorous cleaning measures, led to a reduction in viable Coxiella burnetii spores within the cave’s environment. This, coupled with the Q Fever control program for goats and sheep, including a well-structured vaccination plan, is expected to contribute to diminishing environmental contamination by C. burnetii in the region. 

It is important to note that in regions where Q Fever is endemic, unexpected outbreaks can occur in locations such as natural sites for recreational activities involving animals. Thus, enhancing vigilance, preparedness, and implementing robust surveillance and response capabilities are essential measures to curtail transmission.

As a means of prevention and protection, Coxevac vaccine for ruminants is an effective solution to protect against Q Fever, tackle its reproductive impact and minimize bacterial shedding in ruminants, and therefore safeguarding human health. 


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