Phân biệt dịch bùng phát và dịch lưu hành bằng sinh học phân tử

Tracking strains across time and geography Distinguishing endemic from epidemic disease occurrence Stratification of data to refine study designs Distinguishing pathovars vs commensal f

Tracking strains across time and geography

Distinguishing endemic from epidemic disease occurrence Stratification of data to refine study designs

Distinguishing pathovars vs commensal flora or saprophytes

Identifying new modes of transmission

Studying microorganisms associated with healthcare or institutional infections Surveillance and monitoring response to intervention

Characterizing population distribution and determinants of distribution of parasitic organisms Identifying genetic basis for disease transmission

Validating microdiversity genotyping methods applied to epidemiology

Virus quasispecies population structure analysis

Identifying direction and chain of transmission Identifying hidden social networks and transmission links

Analyzing microbiomes to study non-infectious disease epidemiology

¢Outbreaks provide an opportunity to validate new

Strain typing methods

Once validated, the same method can be applied to investigate other outbreaks and sporadic diseases

¢eWith some infectious diseases, strain typing

methods themselves provide evidence for

occurrence of an outbreak

¢To identify unrecognized outbreaks among what

looks like sporadic (endemic) cases of disease

°To identify vehicles of infection in which

conventional methods are not useful

¢To monitor the impact of an intervention measure

eA small fraction of reported cases come from

recognized outbreaks (7% in salmonellosis in the US)

¢ Identifying risk factors for sporadic infections is difficult

¢ May provide information about attributable risk

¢ May provide information about the dynamics of disease

transmission in a community

¢ transmission by a food vehicle

¢ transmission by person-to-person contact

° geographic and temporal distribution of a clone

Epidemiological question: What is the main source of drug-resistant Salmonella animals

or humans?

1994-95: National Salmonella Antimicrobial Resistance Study

—— (50 state and territories)

1996: National Antimicrobial Resistance Monitoring System

(n=1272) (12 state health dept labs)

1979-80 Salmonella antimicrobial resistance stud

S TYPHIMURIUM CARRYING A 140-Mp PLasmIpD

ANTIBIOGRAM No,

AKSSuTCNCEG ai AKSSuTCN

AKSSUTCE ASSUTCE

AKSSuT 1 ASSuT

KSSuT AKST AST

iP, NJ.NY

iP, Mele

RI

A-AMPICILLIN C-CHLORAMPHENICOL, CE-CEPHALOTHIN

G-GENTAMICIN K-KANAMYCIN N-NITROFURANTOIN

S-STREPTOMYCIN, SU-SULFONAMIDES T-TETRACYCLINE

®

PLASMID PROFILES OF SELECTED MULTIRESISTANT S, TYPHIMURIUM STRAINS

1979-80 ANTIMICROBIAL RESISTANCE STUDY, UNITED STATES

PLASMID PROFILES OF S, TYPHIMURIUM STRAINS RESISTANT To

AMPICILLIN- KANAMYCIN, TETRACYCLINE, STREPTOMYCIN, AND SULFONAMIDES,

1974-75 ANTIMICROBIAL RESISTANCE Stupy UNITED STATES

PLASMID PROFILES OF MULTIRESISTANT S TYPHIMURIUM STRAINS

ISOLATED FROM FAMILY MEMBERS AND A CALF IN AN OUTBREAK,

MoBILE ALABAMA, DECEMBER 197%3

¢Human infections with drug-resistant Salmonella have animal origin

¢ Measures of incidence and prevalence of drug

resistance in a community is dependent on the number

of drug-resistant clones that happen to be circulating in that community at the time of the study

elt is meaningless to discuss increasing or decreasing

prevalence of drug-resistance without specifying the

clonal composition of the isolates tested for

antimicrobial susceptibility.

D9] § đại Fes ` 9

PO

ạve Rivef

Salmonellosis in New Jersey and Pennsylvania, June-Aug, 1981

0 Background:

e Salmonellosis outbreak at a wedding in New Jersey across the river from Philadelphia, Pennsylvania

e Salmonellosis outbreak in a Eye Hospital in Philadelphia

® Precooked roast beef implicated as the vehicle for both outbreaks

® Precooked roast beef prepared

at a meat processing plant in

Philadelphia

Question: How many cases of salmonellosis

caused by precooked roast beef occurred among those not part of these 2 outbreaks?

7.0 1.0.0

chr

S newport from outbreaks, June-

Aug., 1981; case in Pennsylvania (1), case in New Jersey (2), and roast

beef sample in N.J.; 4-6 are sporadic cases with roast beef association

AGAROSE GEL ELECTROPHORESIS OF

S NEWPORT FROM ISOLATED CASES IN PENNSYLVANIA AND NEW JERSEY, JUNE-AUGUST 1981

LANES B8,C,G REPRESENT THE EPIDEMIC STRAINS

WITH 2 PLASMIDS WEIGHING 3.7 AND 3.4 MEGADALTONS

(CHR-CHROMOSOMAL BAND)

Period of isolation Number of isolates

Georgia, Michigan, Texas 45

104

“outbreak period

chr

\

Association between roast beef consumption

and plasmid profile in 19 patients with

Characteristic plasmid profile

® Contaminated food product was introduced into a community

© Increased prevalence ot salmonellosis was found to be associated with one predominant strain of Salmonella

eA single tood product was found to be responsible for nearly 40%

of sporadic salmonellosis cases in NJ and PA in the summer of

1981

e After recall of the implicated food item, salmonellosis caused by

the epidemic clone continued in the community by person-to-

person transmission