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Journal of Clinical Microbiology, February 2007, p. 432-437, Vol. 45, No. 2
0095-1137/07/$08.00+0 doi:10.1128/JCM.01710-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Departments of Gastrointestinal Sciences,1 Community Health, Christian Medical College, Vellore, India,2 London School of Hygiene and Tropical Medicine,3 Virus Reference Department, Centre for Infection, Health Protection Agency, London, United Kingdom,4 Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas5
Received 18 August 2006/ Returned for modification 5 October 2006/ Accepted 20 November 2006
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Rotaviruses are double-stranded RNA viruses comprising a genus within the family Reoviridae. The genome consists of 11 segments of double-stranded RNA that code for six structural viral proteins (VP1, VP2, VP3, VP4, VP6, and VP7) and six nonstructural proteins (NSP1 to NSP6) (7). Rotaviruses are classified into seven different groups (A to G) based on the antigenic specificity of the VP6 capsid proteins. Variability in the genes encoding the outer capsid proteins VP7 and VP4 forms the basis of the current strain typing of group A rotaviruses into G and P genotypes, respectively. At least 15 G genotypes and 26 P genotypes have been identified to date (15).
The epidemiology of rotavirus is complex and varies in different settings. The use of molecular methods has provided increased sensitivity for detection and characterization of unusual strains apart from commonly described genotypes. The G12 strain was first identified and serologically characterized in 1990 from children with gastroenteritis in the Philippines. The strain was not observed again until 2002, when one case each was detected in Thailand (21, 26) and the United States (10). In the following years, more cases of G12 rotavirus infection were described from India (6), Japan (25), Korea (24), and Argentina (3). To date, 45 cases of human G12 rotavirus infection have been described worldwide. Of these, 28 cases were reported among children of <4 years of age in eastern India, including a recent report wherein G12 rotaviruses were found to be responsible for 25 of 147 rotavirus infections (17%), making it the third most common genotype, after G1 and G2, in that area (23).
We have been carrying out concurrent surveillance programs for rotavirus infection and disease in the community and among hospitalized children in Vellore, India, which is in the southern part of the country (1). In this study, we describe a possible outbreak of G12 rotavirus infection in the community and the subsequent detection of the genotype among hospitalized children.
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Hospital-based surveillance. Rotavirus surveillance among children hospitalized with diarrhea was carried out at the Christian Medical College, a 1,800-bed referral hospital in Vellore, India. The number of children under 5 years of age in Vellore is estimated to be approximately 42,000. Children requiring hospitalization for diarrhea were usually residents of the town or of neighboring areas. Stool samples were collected from all children under 5 years of age presenting with acute gastroenteritis and requiring hospitalization for at least 6 h for rehydration. Additionally, stool samples were collected from older children with acute gastroenteritis in whom a viral causative agent was suspected by the attending physician.
Assessment of severity.
Careful scoring of clinical data was carried out for all children. Diarrhea was defined as passage of three or more watery stools in a 24-h period. The severity of diarrhea was assessed with the Vesikari scoring system (22), based on the duration of diarrhea, maximum number of stools passed per day, duration and peak frequency of vomiting, degree of fever, presence and severity of dehydration, and treatment. For calculations of the severity scores for children in the community, a modified Vesikari scoring system was followed. Since accurate temperature measurements were not possible in the field, temperatures were recorded as normal, low-grade fever, and high-grade fever, as reported by caregivers. An episode was considered mild for a score of
5, moderately severe for a score of 6 to 10, and severe for a score of >10.
Laboratory methods. All samples were screened for rotavirus with an enzyme immunoassay for detection of VP6 antigen (Rota IDEIA; Dako Ltd., Denmark) according to the manufacturer's instructions. Viral RNA was extracted from rotavirus-positive fecal suspensions by the guanidine isothiocyanate-silica method described by Boom et al. (2), followed by cDNA synthesis with random primers [pd(N)6 hexamers; Pharmacia Biotech, United Kingdom] and Moloney murine leukemia virus reverse transcriptase (Invitrogen/Life Technologies, United Kingdom). The cDNA was used as a template for G- and P-typing heminested multiplex PCRs using published oligonucleotide primers and methods (8, 9, 11, 12). Purified first-round PCR amplicons for samples for which a G genotype could not be assigned but an 881-bp first-round product was detected were taken for cycle sequencing with fluorescent dideoxy chain terminators (Big Dye terminator cycle sequencing reagent set; Applied Biosystems) and sequenced with an automated genetic analyzer (ABI 310 analyzer; PE Applied Biosystems, Foster City, CA).
Statistical methods. The incidence rates of G12 infection during consecutive time periods were calculated as the number of infections per person time at risk. Age at first infection of G12 was compared to infection with other G types by the Mann-Whitney test. All analyses were done with STATA, version 8.0 (Stata Corp., College Station, TX).
Spatial analysis was performed to determine the incidence of G12 rotavirus infections from birth until March 2006, to detect any clustering of episodes, with SaTScan, version 6.0 (17). The streets and study houses of the urban slums had been mapped and georeferenced previously with ArcView GIS 3.3 (Environmental Systems Research Inc.). The waypoints and trackpoints were collected with GPS Garmin V and downloaded as layers by GPS Utility, version 4.10.4. (GPS Utility Ltd., Southampton, England). Identification of space-time clusters for high rates by the Poisson probability model (16), with a maximum spatial cluster size of 25% of the total population, was done with the equation
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TABLE 1. Clinical and demographic features of G12 cases identified in Vellore, India
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TABLE 2. Comparison of age at first infection of rotavirus G12 with other G-type rotavirus infections detected by multiplex PCR in a community-based birth cohorta
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Calendar time distribution of G12 detection. During the initial 972 child years of surveillance (March 2002 to May 2005), no G12 strains were detected. The first G12 strain was detected on 22 June 2005. The rate of G12 infection was 12.77 (95% confidence interval, 6.75 to 24.55) per 100 child months during June and July 2005. All strains from the community were identified between 22 June and 20 July 2005 from children who lived in adjacent neighborhoods, possibly representing an outbreak with a genotype not detected previously in this setting. Spatial analysis of G12 cases from the community showed a significant space-time cluster involving eight cases within an area of 0.48 km radius during the period of 11 June to 22 July 2005 (relative risk, 676.8; P, 0.001) (Fig. 1). No further G12 strains were detected from the community during surveillance carried out in the following 8 months (August 2005 to March 2006 [292 child years of follow-up]).
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FIG. 1. Space-time clustering of G12 strains in the community, showing the primary cluster of G12 infections during the period of June and July 2005. The circled area is the geographic base of the cylinder (11 June to 22 July), encompassing eight cases of infection; this was determined to be the cluster with the most likely and significant relative risk of infection (RR), 676.8 (within versus outside the cluster).
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History of previous rotavirus infection/disease. There were no records of previous rotavirus infection in hospitalized children, because rotavirus is not routinely tested in children with diarrhea presenting to hospital; however, records of children in the birth cohort were available. Of the five symptomatic children with G12 infection in the community, four had previously documented rotavirus infections. Symptomatic rotavirus infection with the G2P[6] strain was seen in one child, while the other three children previously had asymptomatic rotavirus infections (one G1/G4 strain and two nontypeable strains). Of the four children with asymptomatic G12 infection, two had no previous rotavirus infections, one had an asymptomatic G2P[4] infection, and one had three prior rotavirus infections: a symptomatic infection with the G10P[11] strain and two asymptomatic infections with a G1P[8] strain and a nontypeable strain. The period between previous rotavirus infections and infection with a G12 strain ranged from 9 to 25 months (Fig. 2).
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FIG. 2. Calendar time of rotavirus infections with G12 and other genotypes for the nine children in the community. Each line represents follow-up of a child from recruitment until March 2006. The points at which rotavirus infections were seen are plotted for each child. All G12 strains in the community were identified during June and July 2005. UT, untyped.
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Introduction of a new strain of rotavirus in an urban slum setting presents a potentially high probability of transmission of infection. The slums are overcrowded, with closely clustered houses, many rubbish dumps, and open drains. Sewage and drinking water sources are often close to each other. Defecation close to water sources also increases the possibility of spread of enteric pathogens.
The median Vesikari severity scores of the symptomatic children in the community and hospital were 8 and 11, respectively. These are similar to the severity of rotavirus infection with other G types described previously from the same setting (1). The difference in Vesikari scores among the two groups may be due to an inherent referral bias, as more-severe cases require admission to the hospital. Also, close monitoring of the children in the community children may result in the earlier identification of symptomatic children and prompt treatment. In this study, four cases of asymptomatic infection by G12P[6] were also identified. This is the first report of asymptomatic infection with G12 rotavirus.
The most recent previous study of the molecular epidemiology of rotavirus diarrhea in this setting showed that in 2003 and 2004, P[8] was seen among 15.8% and 55.2% of all rotavirus diarrhea in the community and hospital, respectively. The P[6] genotype was infrequent, detected in 1.2% and 2.2% of infections in the community and hospital, respectively (1). During the period of June to August 2005, P[6] and P[8] were the most prevalent P genotypes seen in both the community and hospital. Seven cases each of P[6] and P[8] infection were seen in the community of 23 rotavirus-positive samples detected in this period. P[8] was seen in combination with G1 (n = 1), G9 (n = 1), G12 (n = 2), and G1/G2 (n = 1), while two samples could not be G typed. P[6] was seen with G genotypes G12 (n = 6) and G2 (n = 1). Of 11 rotavirus-positive samples among hospitalized patients during the same period, four cases each of P[6] and P[8] infection were seen, while three were P[6]/P[8] mixed infections. All four P[6] strains in hospitalized patients were seen in combination with G type G12. The only other P[6] infection was an asymptomatic G2P[6] infection seen soon after a symptomatic G12P[6] infection in a child in the community cohort (Fig. 2). In a setting where P[6] strains have not been frequently described in the past, the detection of a G12P[6] strain may be part of the emergence of a new strain. The less frequent association of G12 with P[8] may be due to virus evolution through reassortment with an already established P type in this setting. This association of G12 strains with different P types can be considered part of its potential evolution toward becoming a stable strain.
The G12 strains described so far have been reported with various P types, such as P[4], P[6], P[8], P[9], or undetermined P types from different parts of the world. This is significant considering the evolution of G9 rotavirus strains. In India, a high incidence of G9P[11] rotavirus infections was initially described (4, 5). These strains were subsequently replaced by G9P[6] strains, which then probably reassorted with human strains of the P[8] VP4 genotype to become G9P[8], now a widely prevalent genotype in India (13). G9 strains have also now been identified as a major global genotype mainly as G9P[8] strains (14); however, these belong to a lineage different from the G9P[11] strains originally described in India.
It is known that nearly every child will experience at least one episode of rotavirus gastroenteritis by the age of 5 (20). Primary infections are believed to be more severe and to occur at a younger age in developing countries (18). In this study, severe rotavirus infection by a G12 strain was seen among children of >2 years of age. Four of the five children with symptomatic G12 infections in the community had previous rotavirus infections. Though the numbers described in this study are small, these infections raise the possibility that there may be no cross-protection against G12 strains from previous rotavirus infections. This may have significant implications for the efficacy of vaccines currently in use in different parts of the world, including recently licensed vaccines from Merck and Glaxo SmithKline and vaccines currently in development. The current vaccines do not include the G12 genotype, and it remains to be determined whether these vaccines will cross-protect against G12 infections. These data reinforce the necessity that a strain surveillance component be included in all countries for monitoring of circulating strains and detection of emerging rotaviruses before and after the introduction of a rotavirus vaccine.
Published ahead of print on 29 November 2006. ![]()
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