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Dispatch
Tularemia Outbreak, Bulgaria,
1997–2005
Todor Kantardjiev,*
Ivan Ivanov,* Tzvetan Velinov,* Plamen Padeshki,* Boris Popov,* Roumiana
Nenova,* and Milcho Mincheff†
*National Center for Infectious and Parasitic Diseases, Sofia, Bulgaria;
and †The George Washington University Medical Center, Washington, DC,
USA
Microbiologic
and Epidemiologic Approaches for Investigation of Outbreak
Epidemiology
After the 1962 outbreak, annual active epidemiologic surveillance was
carried out through a plan worked out by the public health authorities
and included the following: 1) bacteriologic examination of trapped and
dead rodents, 2) bacteriologic examination of water samples, and 3) serologic
examination of patients with unexplainable enlarged lymph nodes.
A total of 285 patients had tularemia from 1997 to 2005. All patients
were initially interviewed by a primary care physician, who sent the patients
to the Hospital for Infectious Diseases (upon tularemia indication) and
the results to the Regional Epidemiology Center. The S1 serum samples
were collected immediately after clinical indication (1–4 weeks after
the onset of symptoms) and the S2 (convalescent-phase) serum samples were
collected 15 ±2 days after the S1. S3 samples were collected 3 months
±15 days after the end of therapy.
The epidemiologic survey included the following information: address,
onset of disease, place of work and possible contact with animals, presence
of dust at the work place, water and food sources, hunting or consumption
of game, and history of tick bite. Questionnaires filled out by the patients
show that they did not drink water from the contaminated wells. The water,
however, was used for irrigating backyard vegetable gardens, and those
vegetables were eaten. Since the human isolates are closely related to
isolates recovered from well water and less to isolates from hares and
ticks, we consider the alimentary route from food by contaminated rodents
or water as the principal one.
Culture Methods
Five hundred milliliters of water were collected in a sterile container.
All subsequent steps were carried out in a class III biosafety cabinet.
The water was centrifuged at 5,000 × g for 10 min. The pellet
was dissolved in 1.5 mL sterile phosphate-buffered saline (PBS) and centrifuged
again as above. The pellet was again dissolved in 1.5 mL PBS. One third
(0.5 mL) was cultured on modified Thayer-Martin agar. Guinea pigs were
passed intraperitoneally with another 0.5 mL, and the remaining 0.5 mL
was kept at –70°C. Guinea pigs were operated on at day 7 or at the
day of exitus. Cultures were made from a homogenized spleen and liver
suspension. Four strains were isolated by the passage method (Appendix
Table).
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Appendix Table. Time,
source, and origin of isolated tularemia strains
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Isolate, source
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Year
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Village
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Region
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Dermacentor-1, tick
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1997
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Aldomirovci
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Slivnitsa
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L1, hare
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1997
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Aldomirovci
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Slivnitsa
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Gal, human
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2003
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Meshtica
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Pernik
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Drag, human
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2003
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Meshtica
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Pernik
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Aqua D, well water
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2003
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Meshtica
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Pernik
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Aqua G, well water
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2003
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Meshtica
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Pernik
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Aqua A, well water
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2003
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Meshtica
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Pernik
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Aqua A, well water
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2003
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Meshtica
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Pernik
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Las, human
|
2004
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Aldomirovci
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Slivnitsa
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Mih, human
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2004
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Aldomirovci
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Slivnitsa
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