2016 Norovirus Outbreak in Spain Linked with Bottled Water

A recent Dispatch article published in the Centers for Disease Control and Prevention (CDC)’s Emerging Infectious Diseases journal, offers insight into a large norovirus outbreak that sprung up in Spain in 2016 that had been linked with bottled spring water.

The Public Health Agency of Catalonia (ASPCAT) reported a staggering 4136 cases of gastroenteritis from April 11, 2016 to April 25, 2016. Of the 4136 cases, 6 individuals required hospitalization. The CDC defines a “case-patient” as an “exposed person who had vomiting or diarrhea (3 or more loose stools within 24 hours),” as well as 2 or more of the following symptoms: nausea, stomach pain, or fever.

ASPCAT investigators traced back the outbreak to contaminated bottled spring water in office water coolers. The water came from a source in Andorra, a small independent principality located between Spain and France. Norovirus is a “very contagious virus,” according to the CDC, and it is common for individuals to become infected by eating contaminated food. Although it’s possible to be infected by consuming contaminated drinking water, this mode of transmission is “rare in developed countries,” according to the article.

The investigators collected water samples from a total of 4 19-L water coolers in 2 different offices located in Barcelona, “from which affected persons had drunk; samples 1 and 2 came from 2 water coolers in one office, while samples 3 and 4 came from 2 water coolers in another office. Using “positively charged glass wool and polyethylene glycol precipitation for virus concentration,” the investigators tested the samples.

“We detected high RNA levels for norovirus GI and GII, around 10³ and 10⁴ genome copies/L, in 2 of the 4 water cooler samples concentrated by glass wool filtration and polyethylene glycol precipitation,” according to the article. The investigators noted that a drawback of using molecular methods is that they are not able to differentiate between particles that are infectious and those that are not. Therefore, they “predicted the infectivity of norovirus in the concentrated samples by treating the samples with the nucleic acid intercalating dye PMA propidium monoazide and Triton X surfactant before RT-qPCR,” which allowed them to “distinguish between virions with intact and altered capsids.”

In those 2 water samples, they found high genome copy values—49 and 327 genome copies/L for norovirus GI and 33 and 660 genomes copies/L for norovirus GII. This was not an unexpected finding, due to the large number of infected individuals associated with the outbreak. Through “PMA/Triton treatment before RT-qPCR assays,” the investigators found that the proportion of infected virions accounted for 0.3% to 5.6% of the total number of physical particles in the water samples, “which was enough to cause gastrointestinal illness.”

The investigators also analyzed fecal samples collected from infected individuals who worked at the office in which the first 2 water samples were collected. They detected the following genotypes in those fecal samples: GI.2 and GII.17. In the fecal samples collected from the other office, they isolated the following genotypes: GII.4/Sydney/2012, GI.2, GII.17, and GII.2.

“We hypothesize that the spring water was contaminated by all 4 strains (GI.2, GII.2, GII.4, and GII.17) but levels of viral contamination for each genotype were not homogeneous in all bottled coolers,” the investigators wrote. “We may have detected only the GII.4 genotype in water samples 1 and 2 because of a higher concentration of this specific genotype or because of bias caused by the sampling, concentration, and molecular detection procedures.”

The investigators admit one limitation to their study: the small number of water samples collected and analyzed. They attribute this to the fact that on April 15, 2016—4 days after the onset of the outbreak—the company that produced the drinking water recalled over 6150 containers of water “of suspected quality” as a precautionary measure. The recall prevented the investigators from collecting more samples to assess, according to the article.

Although the exact cause of the contamination has not yet been identified, the investigators posit that “the high number of affected persons from 381 offices that received water coolers, and the many different genotypes found in some patients’ fecal specimens” suggest that the spring aquifer had been contaminated by “sewage pollution,” and the Andorra Ministry of Health and Welfare banned further use of the spring.

The investigators suggest that assessing commercially-produced mineral waters for different harmful pathogens, such as norovirus would be beneficial. They note, however, that creating, enhancing, and managing such “virus surveillance systems” would be costly. Thus, the investigators suggest taking a “balanced approach to keep both the cost and the time required for the analyses within feasibility limits.”