An Outbreak of Human Astrovirus Lineage 1b in a Middle School in Guangxi, Southern China in 2017
Human astroviruses (HAstVs) are significant etiological agents of viral gastroenteritis worldwide, particularly affecting pediatric patients under the age of five. However, outbreaks of HAstV in middle school settings are relatively rare. This article details an outbreak of HAstV lineage 1b that occurred in a middle school in Guangxi, southern China, in 2017. The outbreak involved 125 adolescents aged 12 to 17 years and was characterized by a range of symptoms, including fever, abdominal pain, diarrhea, and vomiting. The investigation identified the causative agent as HAstV lineage 1b, with a 100% nucleotide identity in the 348-bp region of the capsid protein gene.
The outbreak was first reported on November 7, 2017, when a 14-year-old girl developed fever, headache, and cough. She had no recent travel history or contact with individuals exhibiting similar symptoms. The number of cases increased rapidly, with the first peak occurring on November 9 and 10, with 37 and 30 cases reported, respectively. A second peak began on November 15 and lasted for four days, with 12, 8, 11, and 4 cases reported on each day, respectively. The outbreak subsided after November 18, with no further cases reported. The initial wave of the outbreak was attributed to a common exposure source, while the second wave was likely due to human-to-human transmission.
The clinical presentation of the outbreak included common HAstV infection-associated symptoms such as fever (99.2% of cases), abdominal pain (40.8%), diarrhea (35.2%), and vomiting (6.4%). Additionally, influenza-like symptoms were observed, including headache (48.0%), cough (16.0%), chills (16.0%), runny nose (8.0%), nasal obstruction (7.2%), and pharyngalgia (6.4%). Out of the 125 cases, 122 patients received outpatient treatment, while three required hospitalization. All patients recovered without complications.
To identify the etiological agent, two rounds of sample collection were conducted. Initially, 19 throat swabs were collected from symptomatic students on November 13, focusing on respiratory tract pathogens. These samples were tested for various respiratory viruses, including influenza, human adenovirus, human parainfluenza virus, human rhinovirus, human respiratory syncytial virus, human bocavirus, human coronaviruses, and human enterovirus. Viral RNA was extracted using the viral RNA mini kit, and pathogens were detected using real-time reverse transcription polymerase chain reaction (RT-PCR). Only one sample tested positive for human adenovirus, and three tested positive for human rhinovirus.
A second round of sample collection was conducted on November 16, focusing on diarrhea-associated pathogens. Thirty clinical specimens (rectal and throat swabs) were collected from 16 students and 10 canteen staff, along with five environmental samples from the school canteen. The environmental samples included swabs from the chopping board, kitchen garbage bin, vegetable freezer room, and vegetable refrigerator room. The samples were tested for rotavirus, HAstV, adenovirus, and norovirus using real-time RT-PCR kits. All specimens tested negative for rotavirus and adenovirus, and only one specimen from the canteen staff tested positive for norovirus. However, 13 specimens tested positive for HAstV, including samples from six students, six canteen staff members, and one swab from the chopping board.
To further characterize the HAstV strain, a 449-bp region of the capsid protein gene was amplified using Mon269/Mon270 primers. The amplified products were sequenced, and the resulting nucleotide sequences were found to be 100% identical. The isolate was named 0631/Wuzhou/Guangxi/2017, and the sequence was submitted to GenBank (accession number MH643741). Phylogenetic analysis was performed using the neighbor-joining method and the MEGA7 software program. The analysis revealed that the isolate belonged to the HAstV 1b lineage and was closely related to strains circulating in mainland China after 2015.
The outbreak investigation highlighted several important points. First, HAstV infections can present with both gastroenteritis-like and influenza-like symptoms, complicating the clinical diagnosis. Second, the outbreak in a middle school setting underscores the need for improved hygiene and sanitation measures in schools to prevent the spread of HAstV. The study also identified limitations, including the lack of asymptomatic controls and insufficient sampling for bacterial pathogens, which may have provided a more comprehensive understanding of the outbreak.
In conclusion, the outbreak of HAstV lineage 1b in a middle school in Guangxi, southern China, in 2017, demonstrates the importance of HAstV as a causative agent of acute gastroenteritis in adolescents. The investigation revealed the need for increased awareness and preventive measures to control HAstV outbreaks in school settings. Further research is needed to better understand the epidemiology and transmission dynamics of HAstV, particularly in non-pediatric populations.
doi.org/10.1097/CM9.0000000000000072
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