Applications of Public Health Intelligence:Surveillance

Day 4 Session 2

Dave Jenner EMPHO

July 2009

Surveillance

Spotting things which are:• odd• worrying• threatening• outliers

Surveillance

The systematic, regular collection, analysis, interpretation and dissemination of data for a given population, to detect changes in patterns of disease or disease determinants, with action taken if predefined criteria or thresholds are met.

Surveillance leading to action

The stream fenced off with warning signs

Surveillance - communicable disease

Surveillance - communicable disease

Surveillance - communicable disease

Laboratory-confirmed cases of Measles

England and Wales 2000-2007

2000 100

2001 70

2002 319

2003 437

2004 188

2005 78

2006 740

2007 971

Surveillance - communicable disease

• National Congenital Anomaly System (NCAS) - set up in 1963 in the aftermath of the Thalidomide tragedy.

• NCAS sends alerts to Directors of Public Health if an unusually large number of cases is reported in a given area

Surveillance – congenital anomalies

Source = National Down Syndrome Cytogenetic Register

Down Syndrome Cases in England and Wales

Surveillance – congenital anomalies

Surveillance - cancer

Surveillance - cancerclusters are everywhere and don’t always (or usually) mean there’s a problem

People tend to notice cases first, e.g. four cancer cases on the same street, and then define the population to be studied as only those in that street ...

.... inappropriately drawing a tight boundary around what is probably a chance clustering of a few cases.

A study in California calculated the probability of finding cancer clusters due to chance alone. Theory predicts that 85% of the census tracts in Los Angeles (equivalent to an English electoral ward) would have a significantly raised incidence of at least one type of cancer. That is, we would expect to find over 1,000 ‘clusters’ every year in the Los Angeles area.

The grid on the right shows an actual result of generating 25 random numbers between 1 and 25 and putting a dot in the grid corresponding to each number.

Surveillance - cancer

• How does it work?– the cancer registration system– cancer cluster investigation

http://www.swpho.nhs.uk/resource/item.aspx?RID=9108http://www.cdc.gov/mmwr/preview/mmwrhtml/00001797.htm

Surveillance - cancer

Surveillance - accidents

Surveillance - health care

Surveillance - health care

http://www.sciencelive.org/component/option,com_mediadb/task,play/idstr,CUSP-BAFOS05-06_DavidSpiegelhalter/vv,-2/Itemid,26

Source: BMJ 2003;326:274-276

Surveillance - health care

Surveillance - health care

Applications of PHI: Surveillance

Spotting things which are:• odd• worrying• threatening• outliers