Elizabethkingia anophelis bacteremia is associated with clinically significant infections and high mortality

The genus Elizabethkingia comprises aerobic, non-fermenting, non-motile and non-spore-forming gram-negative rods that were previously named Flavobacterium or belonged to CDC group IIa and later reclassified as Chryseobacterium in 19941. In 2005, Chryseobacterium meningosepticum and C. miricola were transferred to a new genus, Elizabethkingia, on the basis of combined phenotypic and phylogenetic characteristics2. The genus comprises three medically important species, Elizabethkingia anophelis, E. meningoseptica and E. miricola. A novel species, E. endophytica, isolated from sweet corn, was also recently proposed3. E. meningoseptica, previously named Flavobacterium meningosepticum or C. meningosepticum, is the best known species among the genus. E. meningoseptica is a causative agent of nosocomial infections especially in immunocompromised patients, as well as neonatal meningitis and sepsis4. Besides soil, fresh water and plants, the bacterium can be found in hospital environments and may contaminate flushing solutions and medical devices5. Infections caused by E. meningoseptica can be difficult to treat and carry high mortalities, which may be partly explained by their intrinsic multidrug resistance towards commonly used antibiotics such as β-lactams and aminoglycosides6. Therefore, accurate diagnosis is important to guide appropriate antibiotic regimens which often consist of a combination of ciprofloxacin or rifampicin with piperacillin-tazobactam or vancomycin. In contrast to E. meningoseptica, the epidemiology and pathogenicity of E. anophelis and E. miricola were less well understood. E. miricola, originally named C. miricola when first isolated from condensed water obtained from the Russian space station, Mir, only rarely causes nosocomial infections in human7,8. On the other hand, E. anophelis was first isolated from midgut of the mosquito Anopheles gambiae in 20119. Soon after its discovery, it was reported to cause neonatal meningitis in the Central African Republic and a nosocomial outbreak in an intensive-care unit in Singapore10,11. The first discovery of E. anophelis from mosquito gut has raised suspicion on mosquitoes as the source of neonatal meningitis cases in Africa10. However, our recent report on E. anophelis meningitis in two neonates and chorioamnionitis in a neonate’s mother in Hong Kong suggested that mosquitoes were unlikely the vehicles of transmission12. Since the transmission route was initially obscure, draft genome sequencing was performed and showed evidence for perinatal vertical transmission from a mother to her neonate12. The ultimate resolution power of genome sequencing also enabled species confirmation and discrimination from the phenotypically similar species, E. meningoseptica12. Since E. anophelis was commonly misidentified as E. meningoseptica in previous reports10,11,12,13, we hypothesize that many previously described E. meningoseptica isolates were actually E. anophelis and that E. anophelis may account for a significant proportion of Elizabethkingia infections. To better understand the epidemiology and clinical disease spectrum of E. anophelis and Elizabethkingia as a whole, we determined the clinical and molecular epidemiology of bacteremia caused by Elizabethkingia-like species from five regional hospitals in Hong Kong. All bacteremia episodes caused by Elizabethkingia-like species identified by conventional phenotypic tests from 2004 to 2013 during the study period were included. For the 45 episodes of Elizabethkingia-like bacteremia identified, 16S rRNA gene sequencing was performed for species identification and clinical characteristics and outcomes were analyzed.