This document discusses using the H-index to quantify the impact of infectious pathogens in North America. The H-index measures both the productivity and citation impact of published work. It analyzed over 500 pathogens recorded in North America and found H-indices ranged from 0 to 584. Pathogens with the highest H-indices included common bacteria and viruses. Emerging pathogens had significantly higher H-indices than non-emerging. The H-index may be a crude indicator of pathogen emergence and could help prioritize surveillance of emerging threats.

1. The H-index as a quantitative method to
measure pathogen impact in North
America
Ruth Cox
K. Marie McIntyre, Javier Sanchez, Christian Setzkorn,
Matthew Baylis, Crawford Revie

2. Background
Disease surveillance, management and control needs to
assess the relative importance of diseases and pathogens.
Often involves: complex risk assessments
qualitative data
expert opinion
quantitative measurements?

3. Background – The H-index

4. Background – The H-index
• The H-index assesses the quantity and quality of a scientist’s
research output
• Can be calculated automatically using Web of Science (or
other citation databases)
Hirsch JE (2005).
Proceedings of the National Academy
of Sciences of the United States of
America 102(46): 16569-16572.

5. Background – The H-index
• The H-index of a scientific researcher
25
20
Number of citations
15
Citations = Publications = h
10
5
0
0 5 10 15 20 25
Number of publications

6. Background – The H-index
• The H-index of a pathogen reflects the impact of a pathogen
(Mcintyre et al. 2011)
• H-index is correlated with Disability Adjusted Life Year
measurement
Mcintyre KM, Hawkes I, Waret-Szkuta A, Morand S, Baylis M (2011). The H-Index as a
quantitative indicator of the relative impact of human diseases. PlosONE 6(5): e19558.

7. Aim
• To use the H-index to identify and prioritise
infectious pathogens that have the highest impact on
human health in the North American region.

8. Method
• Emerging Infectious Disease Database (EID2)
• www.zoonosis.ac.uk/eid

9. Method
• Emerging Infectious Disease Database (EID2)
www.zoonosis.ac.uk/eid
• Includes information about 6090 pathogens

10. Method
• Two methods were used to identify which pathogens have been recorded
in North America (Canada, United States, Mexico, Greenland).
• Search for pathogens in the National Center for Biotechnology Information (NCBI)
taxonomy website (www.ncbi.nlm.nih.gov/nuccore).
Documents genome sequences and includes geographic location where pathogens have been
isolated.
• Search for pathogens in the PubMed database (www.ncbi.nlm.nih.gov/pubmed/).
Search for publications where the pathogen and North American search terms occurred.

11. Results
• EID2 contains information about 6090 pathogens
• 1828 human pathogen species
• 566 of the 1828 were recorded in the North American region
Pathogen taxonomic group %
Bacteria 42.4
Fungi 22.8
Viruses or prions 18.2
Helminths 10.1
Protozoa 6.5

12. Results
Frequency histogram of the H-index of 566 human pathogens
180
160
140 • H-index ranged from 0 to 584
120 • Median = 38
Frequency
100
80
60
40
20
0
0 50 110 170 230 290 350 410 470 530 590
H-index value

13. Results
Pathogens with the highest H-index
Species H-index Taxonomic
group
Saccharomyces cerevisiae 584 Fungi
Escherichia coli 524 Bacteria
Human immunodeficiency virus 1 410 Virus
Human immunodeficiency virus 2 399 Virus
Hepatitis C virus 289 Virus
Staphylococcus aureus 271 Bacteria
Human herpesvirus 4 257 Virus
Helicobacter pylori 246 Bacteria
Hepatitis B virus 246 Virus
Pseudomonas aeruginosa 243 Bacteria

14. Results
Pathogens with the highest H-index
Species H-index Taxonomic
group
Saccharomyces cerevisiae 584 Fungi
Escherichia coli 524 Bacteria
Yeast – opportunistic infection,
Human immunodeficiency virus 1 410 Virus brewing and baking industry
Human immunodeficiency virus 2 399 Virus Person – person transmitted
Hepatitis C virus 289 Virus bacteria and viruses
Staphylococcus aureus 271 Bacteria Bacteria that cause multiple
clinical infections
Human herpesvirus 4 257 Virus
Food borne pathogen
Helicobacter pylori 246 Bacteria
Hepatitis B virus 246 Virus
Pseudomonas aeruginosa 243 Bacteria

15. Results
• 27.4% of the pathogens were emerging (109/398)
• Emerging pathogens had a significantly higher H-index than non-emerging
pathogens (p<0.001)

16. Results
• 66.1% of pathogens were zoonotic (265/401)
• The H-index of zoonotic pathogens was not significantly different from
non-zoonotic pathogens (p=0.38).

17. Results
Pathogens highlighted as a potential threat to Canada
Greer et al. 2008; Public Agency of Canada (pers. comm.).
* Not recorded in the North America region
Disease/pathogen H-index
Trypanosoma cruzi 130
Nipah virus* 51
Hendra virus* 43
Rift Valley fever virus* 41
Chikungunya virus 39
Monkeypox virus 35
Greer A, Ng V, Fisman D. (2008). Climate change and infectious diseases in North America:
the road ahead. Canadian Medical Association Journal 178: 715-722.

18. Results
• Variation in H-index over time for seven pathogens
160
Chikungunya virus
140
Hendra virus
Monkeypox virus
Nipah virus
120
Rift Valley fever virus
Trypanosoma cruzi
100 West Nile virus
H-index
80
60
40
20
0
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

19. Results
• Variation in H-index over time for seven pathogens
160
Chikungunya virus
140
Hendra virus
Monkeypox virus
Nipah virus
120
Rift Valley fever virus
Trypanosoma cruzi
100 West Nile virus
H-index
80
60
40
20
0
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

20. Results
• Variation in H-index over time for seven pathogens
160
Chikungunya virus
Hendra virus
There is an increasing trend in the total
140
Monkeypox virus number of publications over time
Nipah virus
120
Rift Valley fever virus
Trypanosoma cruzi
100 West Nile virus
H-index
80
60
40
20
0
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Year

21. Conclusion
• Change in H-index may be a crude indicator of pathogen
emergence
• Can it be of practical use in surveillance for emerging
pathogens?
– Time lag between emergence and publication
– Newly emerging pathogens likely to be under represented
– Reflection of trends in interest of pathogens or diseases, research funding,
regional bias

22. Conclusion
• H-index is an indicator of the relative scientific interest in a
pathogen or disease
– Can be used to prioritise pathogens in North America
– Can be incorporated into prioritisation tools and risk assessments
22

23. Added value created by applying a One Health
approach
• The One Health integrative strategy is necessary to manage
today’s complex and interdependent health risks
– The H-index can be used as a measure of the impact of a pathogen
– It is an objective and time efficient method that could be incorporated
in disease prioritisation
23

24. Acknowledgements
Nick Ogden
Alex Demarsh
Phil Hepworth

25. 25

26. The H-index as a quantitative method to
measure pathogen impact in North
America
Ruth Cox
K. Marie McIntyre, Javier Sanchez, Christian Setzkorn,
Matthew Baylis, Crawford Revie