# Presentation: 691538

## West Nile Virus in Chicago, 2002Local Surveillance Issues 

- William S. Paul
- Chicago Department of Public Health

## Plan of Presentation

**Local perspective**
**Crows**: dead crow sightings correlated with subsequent human risk
**Humans**: surveillance for fever & aseptic meningitis had value
**Mosquitoes**: early warning system?

## City of Chicago

- Population 2.9 Million
- Single municipality
- No mosquito abatement district
- Large SLE outbreak in 1975
- WNV detected in Sept, 2001 but no human cases until 2002

## Cases by Week of Onset (N=218)

## Slide 5

## Slide 6

## Case Rates, Selected Local Jurisdictions

| Locality | Pop | Cases | Rate |
| --- | --- | --- | --- |
| St. Tammany, LA | 200k | 39 | 20 |
| St. Louis City, MO | 348k | 56 | 16.1 |
| Cuyahoga, OH | 1.4 M | 215 | 15.6 |
| Suburban Cook, IL | 2.5 M | 387 | 15.6 |
| Oakland, MI | 1.2 M | 181 | 15.1 |
| Chicago | 2.9 M | 203 | 7.1 |

- For illustration only: provisional and unofficial

## CROWS

## Crows vs Human Cases

## AUGUST

**AUGUST**
**10**

## High Crow Mortality Areas

- HCMA – area containing densest 90% of dead crow reports at week 32 (before human cases were known)
- Enlarged to conform to census tracts
- Case-rates then determined in and out of HCMA

## 80.5% of cases within HCMA

- 54.1% of city surface area
- Eventual Case Rates:
- Inside HCMA – 9.4
- Outside HCMA – 3.1

## Dead Birds, Chicago 2002

- Epizootic in the city overlapped epidemic
- Areas with more dead crow sightings had greater subsequent human risk
- Large numbers give more geographic info

## HUMANS

## AUGUST

**AUGUST**
**10**

**Notes:**
Here is a map showing the situation as it stood on August 10.  At this point there is a lot of public anxiety about dead crows.  We are starting to have people becoming ill.  We of course don’t know about these cases until later, after they are diagnosed and reported.  

## Arbovirus Surveillance

-  Human surveillance lab based
- Lab testing prioritized for encephalitis cases, not encouraged or denied for fever
- Positive lab reports announced promptly
- Local effort to classify clinical syndromes, “weed out fever cases”

## Issues in human case surveillance

- Confidence in laboratory is important
- Laboratory reporting timely but sketchy
- Classifying syndromes took substantial follow up

## Clinical PresentationN=221

- Fever anecdotally more “mono-like” than flu-like

## Number of Cases by Age and Diagnosis, (N=220)

- Age

- Cases

- # of

## Case Rates by Age and Diagnosis (N=220)

## Diagnosis by Onset (N=218)

-    July                    August                      Sept.                       Oct.

- 20    27     3      10    17     24    31     7      14     21    28     5      12

## Surveillance for WN Fever

**Pro**
- Increased sensitivity for early cases
- Public health impact
- Already in case counts
- Costly to distinguish syndromes
**Con**
- Milder illness taxes resources
- Convalescent serum specimens (subsequent years)
- Variation in diagnostic access and intensity

## MOSQUITOES

## Pos Mosquito Pools vs Human Cases

## Summary

- Birds: dead crow sightings correlated with subsequent human risk
- Humans: surveillance for fever & aseptic meningitis had value
- Mosquitoes: positive pools concurrent with cases in Chicago, 2002.

## Acknowledgments

**CDPH: Ed Adler, Nicole Cohen, Pam Diaz, Julio Fernandez, Jennifer Garces Sue Gerber, Kevin Gibbs, Eric Jones, Joel McCullough,, Usha Samala, John Watson, **
**IDPH: Connie Austin, Linn Haramis, Carl Langkop **
**CDC:  Roger Nasci, Roy Campbell, Tony Marfin, Duane Gubler**

## THANK YOU