reassessment of a large-scale syphilis epidemic: using an estimated infection date
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Reassessment of a large-scale syphilis epidemic: using an estimated infection date. Schumacher CM, Bernstein KT, Zenilman JM, Rompalo AM Baltimore City Health Department Johns Hopkins University. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Reassessment of a large-scale syphilis epidemic: using an
estimated infection date
Schumacher CM, Bernstein KT, Zenilman JM, Rompalo AM
Baltimore City Health DepartmentJohns Hopkins University
Introduction
• Timely surveillance and early identification of syphilis outbreaks crucial to Elimination Plan
• Epidemic curves illustrate disease dynamics – Traditionally defined by date health department
receives notice of infection– Approach does not account for lag time between date
of infection and date of report
• Hypothesis: Date of infection is more accurate depiction of syphilis dynamics
Introduction, cont’d
• Large outbreak in Baltimore City, Maryland provided model for evaluation of infection date curve
Source: CDC. MMWR. March 2, 1996 45 (8):166-169.
Methods
• Records of early syphilis cases (primary, secondary, early latent) reported to Baltimore City Health Department January 1994 and June 2003
• Stratified by sex and disease stage• 2 epidemic curves
– Date case received by BCHD (report date)– Estimated date of infection (Infection Date)
• Infection Date = Diagnosis Date – Median incubation time– 45 days primary– 60 days secondary– 183 days early latent
Results
• 8409 syphilis cases reported to Baltimore City Health Department (BCHD)
• 7806 (92.8%) diagnosed with Primary, Secondary or Early Latent Syphilis
• 7663 (98%) included in Final Analysis– Exclusions
• 19 (0.2%) missing sex• 1 (0.01%) missing report date• 123 (1.6%) missing diagnosis date
Results (cont’d)
1. Reports fail to account for large increases in infections during development period
2. Report curves do not follow shape or appropriate lag-times during epidemic period
3. Reports underestimate infections during development period
4. Reports overestimate infections during epidemic period
1. Failure to account for increases in infections, P&S syphilis, males
Primary and Secondary Syphilis in Males, Baltimore City, Maryland1993 - 1999
0
20
40
60
80
100
120
140
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er
of
Cases
Report Date Infection Date
For display purposes, data was restricted to years 1993 - 1999
Development PeriodPrimary and Secondary Syphilis in Males
Baltimore City, Maryland 1995
0
10
20
30
40
50
60
70
80
90
1 2 3 4
1995
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
+29% -51%
1. Failure to account for increases in infections, Early Latent Syphilis,
males
Early Latent Syphilis in Males, Baltimore City, Maryland 1993 - 1999
020406080
100120140160180
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er
of
Cases
Report Date Infection Date
Development Period Early Latent Syphilis in Males Baltimore City, Maryland 1995
0
20
40
60
80
100
120
140
1 2 3 4
1995
Year/Quarter
Num
ber o
f Cas
es
Report Date Infection Date
+40%
-48%
2. Report Curve does not reflect shape of infection curve
Primary and Secondary Syphilis in Males, Baltimore City, Maryland1993 - 1999
0
20
40
60
80
100
120
140
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er o
f C
ases
Report Date Infection Date
Epidemic PeriodPrimary and Secondary Syphilis in Males
Baltimore City, Maryland
0
20
40
60
80
100
120
140
1 2 3 4 1 2 3 4
1996 1997
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infefction Date
3. Reports underestimate Infections during development period
• P&S, males– 1Q 1995 – 4Q 1995, 279 infections– 2Q 1995 – 1Q 1996, 232 reports (83%)
• Early Latent, males– 1Q 1995 – 4Q 1995, 386 infections– 3Q 1995 – 2Q 1996, 330 reports (85%)
4. Reports overestimate infections during epidemic period
• P&S, males– 3Q 1996 – 2Q 1997, 370 infections– 4Q 1996 – 3Q 1997, 404 reports (109%)
• Early Latent, males– 2Q 1996 – 1Q 1997, 507 infections– 4Q 1996 – 3Q 1997, 534 reports (105%)
Findings
• Lag-time bias may be present when defining epidemic period based on date of report– Ascertaining changes in demographics and social
factors between pre-epidemic and epidemic periods provides insight into causes and control methods
• Using infection date as timeframe of epidemic removes bias due to incubation time of disease stage and time between diagnosis and reporting
Findings, cont’d
• Difference of curves in 1995 show reporting not prompt after diagnosis– Timely reporting necessary to find and treat
potential contacts before contacts become infectious
– Delayed reporting further impedes Health departments ability to reach contacts, allowing for epidemic propagation
Findings cont’d
• Report overestimation and overlap of curves during epidemic period likely due to increased physician awareness and more intense case seeking
Limitations
• Those in highest risk populations likely not included– Should not bias results since missing from
both curves– Effect on either curve unknown
• Effect of disease stage misclassification also unknown
Conclusions
• Using estimated date of infection as epidemic timeframe more accurate depiction– Understanding community dynamics at time of
transmission may be more useful in determining causes and methods of control especially when overlapping epidemics present
• Comparison on two curves can serve as check on communication between providers and health departments
Recommendations
• With electronic data, algorithm relatively easy, fast and inexpensive
• Health departments should consider using estimated dates of infection as timeframe for epidemic investigations
P&S Syphilis in Males
Primary and Secondary Syphilis in Males Baltimore City, Maryland January 1993-June 2003
0
20
40
60
80
100
120
140
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Quarter/Year
Nu
mb
er o
f C
ases
Report Date Infection Date
P&S Syphilis in Females
Primary and Secondary Syphilis in Females Baltimore City, Maryland
1993 - 1999
0
20
40
60
80
100
120
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er o
f C
ases
Report Date Infection Date
Development PeriodP&S in Females
Development Period Primary and Secondary Syphilis, Females
Baltimore City, Maryland
0
10
20
30
40
50
60
70
80
1 2 3 4
1995
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
+18 %
- 42%
Epidemic PeriodP&S in Females
Epidemic Period Primary and Secondary Syphilis in Females
Baltimore City, Maryland
0
20
40
60
80
100
120
1 2 3 4 1 2 3 4 1 2 3 4
1996 1997 1998
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
Early Latent Syphilis in Males
Early Latent Syphilis in Males Baltimore City, Maryland
1993 - 1999
020406080
100120140160180
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er o
f C
ases
Report Date Infection Date
Epidemic PeriodEarly Latent in Males
Epidemic Period Early Latent Syphilis in Males
Baltimore City, Maryland
0
20
40
60
80
100
120
140
160
180
1 2 3 4 1 2 3 4
1996 1997
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
Early Latent Syphilis in Females
Early Latent Syphilis in Females Baltimore City, Maryland
1993 - 1999
0
20
40
60
80
100
120
140
160
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
1993 1994 1995 1996 1997 1998 1999
Quarter/Year
Nu
mb
er o
f C
ases
Report Date Infection Date
Development PeriodEarly Latent in Females
Development Period Early Latent Syphilis in Females
Baltimore City, Maryland
0102030405060708090
100
1 2 3 4
1995
Year, Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
+ 96%
-46%
Epidemic PeriodEarly Latent in Females
Epidemic Period Early Latent Syphilis in Females
Baltimore City, Maryland
0
20
40
60
80
100
120
140
160
1 2 3 4 1 2 3 4 1 2 3 4
1996 1997 1998
Year/Quarter
Nu
mb
er o
f C
ases
Report Date Infection Date
Reports underestimate infections during development period
• P&S Females– 1Q 1995 – 4Q 1995, 204 infections– 2Q 1995 – 1Q 1996, 152 reports (75%)
• Early Latent, Females– 1Q 1995 – 4Q 1995, 301 infections– 3Q 1995 – 2Q 1996, 258 reports (86%)
Reports overestimate infections during epidemic period
• P&S, Females– 3Q 1996 – 2Q 1997, 323 infections– 4Q 1996 – 3Q 1997, 346 reports, (107%)
• Early Latent, Females– 1Q 1996 – 3Q 1997, 797 infections– 3Q 1996 – 1Q 1998, 862 reports, (108%)