A predominant role for Norwalk-like viruses as agents of epidemic gastroenteritis in Maryland nursing homes for the elderly

Abstract

Stool specimens from 156 Maryland nursing home residents, who became ill during 20 outbreaks of gastroenteritis from November 1987 through February 1988, were analyzed. All tested negative for astroviruses, enteroviruses, Group A rotaviruses, Sapporo-like caliciviruses, and enteric bacteria (i.e., Salmonella, Clostridium, and Shigella species). Eighty-two (52%) were positive for Norwalk-like viruses (NLVs), members of the family Caliciviridae. Six distinct genetic clusters within genogroups I and II of the NLVs were detected; a genogroup II (GII) virus closely related to the Camberwell virus in the NLV GII/4 genetic cluster was the predominant strain. Serologic evidence of infection with > or = 1 NLV was detected in 61 (56%) of 109 patients tested against 3 NLV antigens (i.e., Norwalk, Hawaii, and Toronto viruses). Sixteen (80%) outbreaks met the definition for an NLV outbreak. Taken together with a retrospective analysis of bacterial gastroenteritis in this same setting, these data support a major role for NLVs as etiologic agents of gastroenteritis in elderly persons.

Figure 1

Comparison of the monthly distribution of 840 outbreaks of acute presumed viral gastroenteritis (GE) outbreaks (blue) and 24 outbreaks of acute bacterial GE outbreaks of Salmonella (red), Clostridium difficile (pink), and Shigella (green) species reported to the Maryland State Department of Health and Mental Hygiene over a 15-year period (1986–2000).

Figure 2

Phylogram created with the DISTANCES and GROW-TREE programs (both part of the Genetic Computer Group suite [Oxford Molecular Group] [51]), using the uncorrected distances algorithms, on the basis of the alignment of 176 bases near the 5′ end of open-reading frame 2. The GenBank numbers of the reference strains are Bristol (X76716), Lordsdale (X86557), Camberwell (U46500), Hawaii (U07611), Melksham (X81879), Hillingdon (AJ277607), Amsterdam (AF195848), Leeds (AJ277608), Toronto (U02030), Sea-croft (AJ277620), Alphatron (AF195847), Musgrove (AJ277614), Chiba (AB022679), Southampton (L07418), Hesse (AF093797), Norwalk (M87661), Desert Shield (U04469), and Winchester (AJ277614). The scale bar represents 10 substitutions per 100 residues.

Figure 3

Alignments base don the entire open-reading frame 2-aa sequences of the nursing home and reference viruses, using the PILEUP and PRETTY programs from the Genetic Computer Group suite (Oxford Molecular Group) [51]. The GenBank numbers of the reference viruses in panel A are OTH-25 (L23830), MXV (U22498), TV (U07611), Rbh (A89098), AUV (U46039), Arg320 (AF190817), and Bham132 (CAB89092). GenBank numbers of the reference viruses in panel B are LV (X86557), BV (X76716), CV (AF145896), 364/1996/AZ (AF080553), 379/1996/AZ (AF080556), 345/1996/SC (AF080549), 358/1996/FL (AF080552), 366/1996/ID (AF080554), 408/1996/FL (AF080558), PRV (AJ27761), GRV (AJ004864), and SYV (AJ277619). AUV, Auckland virus; GRV, Grimsby virus; PRV, Park Royal virus; SYV, Symgreen virus. Regions that correspond to the N (N-terminal), S (shell), P1 (protruding), and P2 structural domains of the Norwalk virus capsid protein that were defined by Prasad et al. [60] are indicated.

Figure 3

Alignments base don the entire open-reading frame 2-aa sequences of the nursing home and reference viruses, using the PILEUP and PRETTY programs from the Genetic Computer Group suite (Oxford Molecular Group) [51]. The GenBank numbers of the reference viruses in panel A are OTH-25 (L23830), MXV (U22498), TV (U07611), Rbh (A89098), AUV (U46039), Arg320 (AF190817), and Bham132 (CAB89092). GenBank numbers of the reference viruses in panel B are LV (X86557), BV (X76716), CV (AF145896), 364/1996/AZ (AF080553), 379/1996/AZ (AF080556), 345/1996/SC (AF080549), 358/1996/FL (AF080552), 366/1996/ID (AF080554), 408/1996/FL (AF080558), PRV (AJ27761), GRV (AJ004864), and SYV (AJ277619). AUV, Auckland virus; GRV, Grimsby virus; PRV, Park Royal virus; SYV, Symgreen virus. Regions that correspond to the N (N-terminal), S (shell), P1 (protruding), and P2 structural domains of the Norwalk virus capsid protein that were defined by Prasad et al. [60] are indicated.

Figure 4

Variations in amino acids between MD145-12 and Camberwell virus (CV). Blue and red bars indicate the conservative and nonconservative amino acid substitutions, respectively. Arrows and numbers indicate the location of the putative proteolytic cleavage sites within the open-reading frame 1 nonstructural polyprotein and are based on the previously identified cleavage sites of the Southampton and Camberwell viruses [61, 62].