during march 31april 6 , 2014 , in honiara , a tropical depression caused 663 mm of rainfall , 10 times the mean weekly rainfall recorded during 20102013 ( 6 ) . after the flooding event , use of the pacific syndromic surveillance system ( psss ) ( 7 ) , which collects weekly aggregated data on diarrhea and other syndromes from 4 health facilities in honiara and 4 provincial hospitals , was transitioned to a postdisaster early warning alert and response surveillance network ( ewarn ) to enhance outbreak detection and response ( 8) . to characterize the outbreak , we identified nonbloody ( > 2 loose bowel movements in 24 hours ) and bloody ( any episode of loose bowel movement with visible blood ) diarrhea from psss / ewarn databases and patient registries of 10 outpatient and inpatient facilities in honiara and 6 provincial hospitals from the outbreak period , april 7july 13 , 2014 . to verify that this was an outbreak and not normal seasonal fluctuation , we also reviewed longitudinal diarrhea data from psss sentinel sites during january 2013august 2015 . the national referral hospital ( nrh ) in honiara evaluated fecal samples from inpatients and outpatients who had diarrheal illness . samples were routinely tested for salmonella enterica , shigella spp , vibrio cholera , and rotavirus . a rapid diagnostic test ( rdt ) , the sd bioline yongin , south korea ) , was used to test for rotavirus at the nrh ( 9 ) . we genotyped rotavirus - positive samples as previously described ( 10 ) and calculated incidence rates using the solomon islands 2009 census . negative binomial regressions and fisher exact testing evaluated differences in rates and proportions testing positive . we identified 4,087 diarrhea cases from the city of honiara during the outbreak period , of which 3,664 cases ( 90% ) were nonbloody . the mean number of weekly cases of diarrhea among psss sites in honiara increased from 81.7 to 236.5 ( rate ratio 2.90 , 95% ci 2.133.96 ) from baseline to outbreak and baseline periods . the highest attack rate during the outbreak occurred in the < 5 years age group ( 32% ) , which was > 14 that observed for the 5 years age group ( 2% ) . during the outbreak , 6 of 9 provinces in the solomon islands reported diarrhea outbreaks , comprising the flood - affected province of guadalcanal and 5 provinces that were not affected by the tropical depression and flooding ( malaita , makira , western , isabel , and choiseul ) ( figure 1 , panels c  e ) . hospital - based surveillance identified 4,407 diarrhea cases , of which 1,626 ( 37% ) were reported from provinces unaffected by flooding . during the outbreak , 27 diarrhea - related deaths were identified , including 10 from flood - affected provinces ( 3.6 deaths/1,000 case - patients ) and 17 from provinces where no flooding occurred ( 8.6 deaths/1,000 case - patients ) . of the 23 deaths with information on age , 21 ( 91% ) were < 5 years . among 61 fecal samples collected during the outbreak in honiara , 23 ( 38% ) tested positive in the rotavirus rdt , versus none of the 43 samples collected during the same period in 2013 ( p<0.001 ) ( table 2 ) ; the proportion positive for other pathogens tested was similar for 2013 versus 2014 . of 5 samples collected in june during the outbreaks in non - flood  affected areas , 4 tested positive in the rotavirus rdt ; each of the 4 positive samples were obtained from a different province ( choiseul , isabel , makira , and malaita ) . isolates from the 4 samples were identified as genotype g9p and found to have identical vp4 and vp7 sequences ( genbank accession nos . the vp7 isolates were most similar to strains circulating in china and russia during 20112013 ( figure 2 ) . * samples were collected and tested at the national referral hospital , honiara ; no rotavirus tests were conducted during the outbreak period in 2015 . nucleotide sequence  based phylogenetic tree of rotavirus viral protein ( vp ) 7 for isolates obtained in the solomon islands during an outbreak of diarrheal illness after flooding in the capital city of honiara . we visually analyzed generated electropherograms and constructed contiguous dna sequence files using the sequencher software program version 5.0.1 ( gene codes corp inc . , ann arbor , mi , usa ) . we performed nucleotide similarity searches using the blast ( http://www.ncbi.nlm.nih.gov ) and compared the nucleotide and deduced amino acid sequences of the vp7 gene with sequences available in genbank possessing the entire open reading frame . we constructed multiple nucleotide and amino acid alignments using the muscle algorithm in mega 6.0 ( http://www.megasoftware.net/ ) . nucleotide and amino acid distance matrices were calculated by using the p - distance algorithm in mega 6.0 . we selected the optimal evolutionary model based on the akaike information criterion ( corrected ) ranking implemented in jmodeltest ( github , heidelberg , germany ) and generated maximum - likelihood phylogenetic trees using the nucleotide substitution model trn+gamma 4+i in mega 6.0 , and assessed the robustness of branches by bootstrap analysis using 1,000 pseudoreplicate runs . we report a nationwide epidemic of diarrhea in the solomon islands , which was precipitated by a focal extreme weather event . disasters can facilitate transmission of infectious diseases through population displacement , overcrowding , limited access to clean water , and compromised hygiene and sanitation ( 3 ) . an assessment to quantify the risk for disease outbreaks was done immediately after the floods and identified a high risk for diarrheal outbreaks in honiara and guadalcanal ( e.j . nilles , unpub . data ) . using protocols developed after a tsunami emergency in 2013 ( 11 ) and insight gained by the experience , the ministry of health and medical services rapidly established an ewarn to strengthen disease detection and response capabilities . we report an increase in diarrheal cases shortly after the floods , and despite implementation of control measures , large outbreaks were detected in the flood - affected areas of honiara and other parts of guadalcanal . we subsequently identified outbreaks in multiple areas not affected by the flooding , indicating transmission from flood to non - flood affected areas . the proportion of rotavirus - positive samples was 38% during 7 april13 july , 2014 , versus 0% during the same period in 2013 , and increased to 55% during the peak of the outbreak from april 28may 11 . outbreaks in non - flood affected provinces began soon after the peak of rotavirus transmission in honiara . illness and deaths caused by rotaviruses primarily affect the < 5 years age group , unlike most other diarrheal agents with epidemic potential that affect all age groups ( e.g. , vibrio cholera , shigella dysenteriae , norovirus ) ( 12 ) . finally , all 4 isolates from 4 non - affected provinces demonstrated 100% genetic homology of target genes , consistent with a common origin . however , the small number of diarrheal samples tested for a small number of pathogens limited our ability to conclusively define the role of rotavirus versus other diarrheal pathogens . there was limited historical baseline data against which to compare our findings , but given the consistent collection of data through the psss during 201315 , and the direct observations of multiple study authors ( who were involved in outbreak response activities ) of substantial surges in diarrhea cases throughout the country , we are confident that this was an outbreak and not seasonal fluctuation . we only included ambulatory cases and did not evaluate hospitalizations . improved understanding of the health implications of changing climate patterns is necessary to drive evidence - based mitigation strategies . post - disaster early warning alert and response networks can ensure the rapid detection of , and response to , disease outbreaks that are likely to increase as climate change leads to more severe extreme weather events . countries at risk for extreme weather events and other disasters , including many pacific island nations , should ensure protocols and plans have been tested and are in place and to rapidly enhance disease detection and response capacities . rotavirus may cause or contribute to epidemics in the post - disaster setting , emphasizing the importance of implementing global childhood rotavirus immunization guidelines ( 13 ) .
flooding on 1 of the solomon islands precipitated a nationwide epidemic of diarrhea that spread to regions unaffected by flooding and caused > 6,000 cases and 27 deaths . 
 rotavirus was identified in 38% of case - patients tested in the city with the most flooding . 
 outbreak potential related to weather reinforces the need for global rotavirus vaccination .