Noroviruses - which are often mistakenly called `stomach flu’ - are single-stranded RNA viruses that (like influenza) are able to evolve rapidly. So we typically see a new dominant norovirus strain emerge every two or three years. In 2009, we saw the emergence of the New Orleans strain of GII.4, while in 2012, the Sydney strain appeared.
Victims usually experience nausea, frequent vomiting & diarrhea, and stomach pain – and may also suffer from headache, fever, and body aches.
Outbreaks from these viruses are the bane of cruise ships, schools, and hospitals – anywhere large numbers of people congregate. While the illness usually runs its course in 1 to 3 (very long) days - among those who are aged or infirmed -the virus can take a heavy toll.
According to the CDC, in the United Sates each year the norovirus:
- causes about 21 million cases of acute gastroenteritis (inflammation of the stomach or intestines or both)
- contributes to about 70,000 hospitalizations and 800 deaths, mostly among young children and the elderly
With new strains appearing every few years, and most requiring a ridiculously low infectious dose, the ability for norovirus to spread is legendary. In Vomiting Larry And His Aerosolized Norovirus, we looked at work done by the UK’s Health and Safety Laboratory, where they created a robot that . . . you guessed it . . . vomits.
By adding a florescent dye marker to robot’s `vomitus’, researchers have determined that droplets – too small to be readily seen – can end up as far as 3 meters away from the source.
The `standard’ mode of norovirus transmission is considered to be the fecal-oral route, but limited airborne transmission is increasingly being considered a factor.
The CDC – in a an MMWR report from 2011 called Updated Norovirus Outbreak Management and Disease Prevention Guidelines describes transmission thusly:
Norovirus is extremely contagious, with an estimated infectious dose as low as 18 viral particles (41), suggesting that approximately 5 billion infectious doses might be contained in each gram of feces during peak shedding. Humans are the only known reservoir for human norovirus infections, and transmission occurs by three general routes: person-to-person, foodborne, and waterborne.
Person-to-person transmission might occur directly through the fecal-oral route, by ingestion of aerosolized vomitus, or by indirect exposure via fomites or contaminated environmental surfaces.
While the numbers change almost years, there are currently 6 identified genogroups of norovirus (GI-GVI). GI and GII genogroups are known to infect humans, and GI has 9 known genotypes, while GII has 22.
The most common source of human infection for more than a decade has come from Genogroup II, genotype 4 (abbreviated as GII.4).
Yesterday, however, the CDC’s EID Journal carried a dispatch describing a recently emerged GII.17 strain. Although sporadic GII.17 cases have been previously reported in Africa, Korea, Taiwan, and Japan, the first major outbreak was documented in Guangzhou last November, and it is now reportedly spreading rapidly across China.
Gastroenteritis Outbreaks Caused by Norovirus GII.17, Guangdong Province, China, 2014–2015
Jing Lu1, Limei Sun1, Lin Fang, Feng Yang, Yanling Mo, Jiaqian Lao, Huanying Zheng, Xiaohua Tan, Hualiang Lin, Shannon Rutherford, Lili Guo, Changwen Ke, and Li Hui
In the past decade, the most prevalent norovirus genotype causing viral gastroenteritis outbreaks worldwide, including China, has been GII.4. In winter 2014–15, norovirus outbreaks in Guangdong, China, increased. Sequence analysis indicated that 82% of the outbreaks were caused by a norovirus GII.17 variant.
Norovirus infection is a leading cause of nonbacterial gastroenteritis outbreaks in industrialized and developing countries (1,2). On the basis of amino acid identity in viral protein 1, noroviruses can be divided into at least 6 genogroups (GI–GVI). GI and GII infect humans and can be further classified into genotypes; at least 9 genotypes belong to GI and 22 belong to GII (3). During the past decade, most reported norovirus outbreaks were caused by GII.4 norovirus (4,5). New variants of GII.4 have emerged approximately every 2–3 years and have caused norovirus gastroenteritis pandemics globally (6). Since 1999, the major circulating genotype in mainland China has been GII.4, accounting for 64% of all genotypes detected (7). In winter 2014–15, norovirus outbreaks in Guangdong Province, China, increased. Sequence analyses showed that the major cause of continuous gastroenteritis outbreaks in the region was a rarely reported norovirus genotype: GII.17.
Sequence comparison with archived GII.17 strains from GenBank suggests that the GII.17 genotype identified in Guangdong is a newly emerged variant, differing from GII.17 strains detected before 2011. The recent detection of this new variant in samples from patients with sporadic cases in several regions of Asia (e.g., Korea, Japan, and Taiwan) and from groundwater in Kenya (11) suggests that this variant of GII.17 has circulated in a wide range of areas in recent years. For GII.17, most (66 [83%] of 80) sequences from the GenBank database are restricted to region C, the short conserved sequences of the N terminus of the capsid gene. This conserved region has been widely used for genotyping strains (12) and phylogenetic studies (13). To include more reference strains and to illustrate the relationship between GII.17 from Guangdong and other regions, we mainly used region C for phylogenetic analyses in this study. Similarly, phylogenetic analysis based on the nearly full length of capsid sequences also showed that the newly emerged GII.17 variant in Guangdong clustered with the strains from Japan and Taiwan in 2013 and 2014 and differed from GII.17 strains detected before 2011 (Technical Appendix[PDF - 159 KB - 2 pages] Figure 2).
In conclusion, a norovirus genotype GII.17 variant emerged in winter 2014–15 and caused outbreaks in multiple cities in Guangdong Province, China. The distribution of GII.17 genotype among patients with sporadic cases of gastroenteritis remains unknown. In future studies, epidemiologic and virologic surveillance should be broadened to better clarify virologic, clinical, and epidemiologic patterns of this newly emerged norovirus.
Of note, GII.17 made news last summer in Norovirus GII.17 Predominates in Selected Surface Water Sources in Kenya and was suspected as the cause of an outbreak recently in Taiwan.
Whether GII.17 spreads as rapidly, and as thoroughly, as the Sydney GII.4 strain that emerged in 2012 remains to be seen, but the timing is right for seeing a new strain take hold.
One of the keys to prevention is good hand hygiene, unfortunately, unlike with many other bacteria and viruses, alcohol gel doesn’t do a particularly good job of killing the virus (see CMAJ: Hand Sanitizers May Be `Suboptimal’ For Preventing Norovirus).