Should we recommend precautions during a hantavirus endemic?

Sir,

The number of notified hantavirus infections in southwestern Germany increased considerably in the beginning of the year 2007; therefore, the German health institutions put out a press release in the areas with the highest incidence in the southwestern part (Baden-Wuerttemberg) to establish precautions in the case of a possible contact with rodents [1].

During this significant endemic burst of infections, a 43-year-old male patient presented in Baden-Wuerttemberg with fever (>39°C), low back pain and acute renal failure. He told the doctors at the emergency department that he most likely had a hantavirus because he had cleaned his garden cabin 10 days before the presentation in the emergency department, and he had observed several rodents in his garden in the past. Because of the mentioned press release of an increased number of hantavirus infections with a broad discussion in the public, he followed some of the recommended precautions of the governmental health institutions and used a disposable respirator of category 1 (FFP1) during the cleaning procedure [2]. On clinical examination, the patient was afebrile, his blood pressure was 135/90 mmHg, and the initial laboratory investigations showed a low platelet count (65 × 109/L), normal electrolytes and an elevated serum creatinine (4.8 mg/dL). Hantavirus-specific IgM antibodies (Puumala) were strongly positive and IgG slightly positive. The infection was self-limiting, with a maximum serum creatinine of 4.8 mg/dL and a normalization of the kidney function tests in the follow-up.

Hantaviruses comprise one of five genera of the family Bunyaviridae, and the natural reservoirs are rodent-borne pathogens [3]. Human infection occurs most commonly through the inhalation of infectious, aerosolized saliva or rodent faeces. In Europe and Asia, hantavirus infections can present with a haemorrhagic fever and renal syndrome (HFRS). The main hantavirus species in Germany is Puumala, and their main reservoir is bank voles (Myodes glareolus), which predominantly live in temperate forests of Western and Central Europe or in the boreal forests (taiga) in Northern Europe. It is reported that, in endemic areas, the incidence of hantavirus infections among humans is related to the size of the bank vole population and prevalence of the virus [4,5]. Every 3–4 years, there are peaks in the bank vole population, and this may result in an increase in human infection rates. In Germany, laboratory-confirmed symptomatic hantavirus infections are mandatorily notifiable since 2001. In the period from 1 January 2007 to 3 June 2007, 526 symptomatic hantavirus cases were reported to the Robert Koch Institute. In the comparable time period of the previous years, the mean number of reported cases was only 71 (minimum in 2006 with 17 cases and maximum in 2005 with 171 cases), this is a seven times higher incidence, and the vast majority of cases (77%, 405 cases) were reported from Baden-Wuerttemberg [2]. The Robert Koch Institute and a recent overview of Clement et al. from the Hantavirus Reference Center in Belgium explained this significant increase of hantavirus infection by an extraordinarily mild winter 2006/2007 with no snow cover on the ground and, additionally, an abundant supply of beech mast in the autumn of 2006 (the so-called ‘mast hypothesis’) [5]. This could have resulted in an early increase in the bank vole population because of higher rodent survival rates, and the breeding could have started earlier. Furthermore, during the mild winter 2006/2007, humans may have been more exposed to rodents because of increased outdoor activities [1]. During this extraordinary increase, the issue of infection prevention was discussed in the public media (press and television), and the government health institutions sent bulletins to the physicians in the endemic areas, especially in Baden-Wuerttemberg [6].

The prevention–recommendation of the Robert Koch Institute in Germany in a high-risk situation was

(i) reduce dust development in contaminated areas, e.g. by moistening;

(ii) use disposable gloves and, if dust development is not avoidable, use disposable respirators;

(iii) if you have observed rodents, ventilate closed rooms for 30 mins and eventually use disposable respirators and gloves; and

(iv) use disinfection fluids.

The Center for Disease Control and Prevention (CDC) recommendations in the USA are more detailed; one reason could be the more serious clinical manifestation by the different hantavirus species in the USA [3,7].

Our well-informed patient considered the planned cleaning of his garden cabin as a high-risk situation (observed rodents in his garden in the past) and tried to prevent an infection by wearing a disposable respirator and gloves as proposed by the health institutions [2,7]. This prevention failed, and he developed, after the usual incubation period, the feared infection.

This case raises several questions: Did our patient use incorrect preventative measures, or not enough of the preventative measures needed? What is the value of the proposed prevention recommendations? Should we recommend precautions during a hantavirus endemic?

The most likely explanation in the failed prevention in our patient is the missing ventilation of his garden cabin for 30 mins before starting to clean. Ventilation of a confined space (hut, cabin, attic, etc.) with a presumed presence of rodents (e.g. during the past winter) is the most effective, easiest and least expensive protective measure. The floors must be sprayed with water and bleach; afterwards, it is recommended to flush with water and to avoid sweeping in order to avoid breathing rodent excreta.

The value of the proposed FFP1 has to be discussed because in theory, protection against a biohazard requires at least a FFP2 mask with a high-efficiency particulate absorption or arrestance (HEPA) filter. HEPA filters remove at least 99.97% of airborne particles 0.3 µm in diameter. Although an individual virus particle ranges in size from 0.005 to 0.1 µm, viruses generally only survive to travel through the air as part of larger particles (0.3 µm or larger), for example, attached to mucous particles. FFP1 masks are not 100% effective in protecting against aerosolized viruses, as apparently proven in this case. The use of FFP2 masks in the general public, however, is deemed to expensive and impractical.

Up to now, it is difficult to give exact recommendations. On the one hand, the incidence of a severe hantavirus is still low, and hysteric precautions during all leisure activities will not be helpful, especially because gardening in urban areas and exercising/recreational activities in the forest (like jogging) showed no increased risk in a case-control study [8]. On the other hand, a well-informed society can try to avoid high-risk situations by simple and cheap measures [9], and hopefully, the infection rates can be reduced: avoid camping or sleeping on grounds with many rodent burrows, turn your back to the wind when working on such grounds or when cutting wood in the forest, ventilate indoor locations with signs of rodent manifestations, and after ventilation, wet mop floors with a bleach solution.

In summary, in order to establish more detailed prevention recommendations, the nephrology community has to learn more about risk factors and detailed infection route circumstances.

Conflict of interest statement. None declared.