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on august 19 , 2013 , two persons from sancaktepe village , turkey , sought care for influenza - like symptoms , tonsillitis , and swollen neck lymph nodes .
clinicians treating the patients did not perform lymph node biopsies or conduct pcr testing of blood specimens to identify f. tularensis . over the following weeks ,
we conducted an investigation to identify potential exposures leading to f. tularensis infection ( of any clinical form ) among sancaktepe village residents .
we defined a suspected case as onset of > 1 specific symptoms ( swollen lymph nodes in the neck or periauricular areas , sore throat , or swelling or redness of eyes ) or > 2 nonspecific symptoms ( fever , chills , myalgia , or headache ) during july 1august 1 , 2013 .
a confirmed case was a suspected or probable case with a positive serologic test result .
specific antibodies in patients blood ; a titer > 1:160 was the cut - off ( 2 ) . because of inadequate laboratory capacity to handle heavily polluted water , we used culture , but not pcr , to identify f. tularensis in implicated environmental samples . of 350 sancaktepe
village residents , we excluded 46 who were absent during ramadan 2013 , the likely exposure period ( explained in the next paragraph ) . from the remaining 304 residents , we identified 122 suspected case - patients , of whom 94 underwent blood microagglutination testing ; 39 were positive ( titers 1:1601:2,560 ) for f. tularensis .
no patient had a 4-fold rise in antibody titers between acute and convalescent phases of illness . on the basis of symptoms
, we identified 16 additional probable cases among suspected case - patients who were not tested ( 7/13 ) or who had a negative microagglutination test result ( 9/24 ) .
the 55 confirmed or probable cases / case - patients are henceforth referred to as cases / case - patients .
the outbreak began on july 9 , peaked in late july , and ended in early september 2013 .
the epidemic curve indicated a continuous common - source exposure and a likely exposure period that roughly coincided with ramadan 2013 ( july 8august 7 ) ( figure ) .
cases occurred in all age groups ( technical appendix table 1 ) and village - wide .
the attack rate did not differ significantly by sex : 18 ( 13% ) of 137 male residents and 37 ( 22% ) of 167 female residents were infected ( relative risk [ rr ] 1.6 , 95% ci 0.932.6 ) .
clinical signs and symptoms included influenza - like symptoms and swollen lymph nodes in the neck or preauricular regions ( technical appendix table 2 ) .
epidemic curve indicating a continuous common - source exposure leading to an outbreak of oropharyngeal tularemia , sancaktepe village , turkey , july 
we hypothesized that the outbreak was caused by waterborne bacteria for 3 reasons : case - patients predominantly had oropharangeal symptoms ; case - patients age and geographic distributions suggested a ubiquitous exposure ; and villagers reported that the tap water had a dead - animal smell during ramadan . a retrospective cohort study ( excluding 46 persons with sore throat or swollen lymph nodes but
not meeting definitions for probable or confirmed case - patients ) showed that illness developed in 27% ( 46/173 ) of persons who drank tap water versus 11% ( 9/85 ) of persons who did not ( rr  2.5 , 95% ci  1.34.9 ) .
sensitivity analyses showed slightly stronger associations between drinking tap water and illness when only confirmed cases ( rr  3.4 , 95% ci  1.48.4 ) or cases with onset during the week of july 22 ( rr  3.0 , 95% ci  1.18.4 ) were included . *
the outbreak was associated with ramadan , which occurred during july 8august 7 , 2013 .
we asked villagers whether they had engaged in game hunting or eaten game meat around ramadan ; no villagers had such exposures .
in addition , according to the village administrator , no large , village - wide gathering had occurred around ramadan .
inspection of the village s main water storage tank revealed that the solar - powered chlorination device had malfunctioned .
water collected on august 22 had a chlorine level of 0 and elevated levels of total coliform ( 60 colony - forming units [ cfus ] ) and escherichia coli ( 1 cfu ) .
the main water storage tank was supplied by 2 water collection sites , a and b. water from site a had unremarkable findings and low turbidity .
collection site b had 3 sources of water , 1 of which was surface water .
rodent activities , but not dead animals , were evident near the surface water ditch .
water samples collected from site b on august 22 had high levels of total coliform ( > 100 cfu ) and e. coli ( 50 cfu ) ( technical appendix figure ) .
culture of 2 water samples collected on august 28 and september 4 , respectively , did not yield f. tularensis .
more than 300 wild and domestic animals worldwide have been found to be naturally infected with f. tularensis ( 1 ) .
holarctica , the only known disease - causing subspecies in eurasia ( 5 ) , is associated with water - associated rodents ( e.g. , beavers , muskrats ) .
humans can be infected with this subspecies by drinking contaminated water ; having contact with contaminated streams , lakes , or rivers ; having direct contact with contaminated objects ( 1,2 ) ; or eating uncooked contaminated food ( 6 ) .
tularemia surveillance in turkey reported 4,827 tularemia cases nationwide during 20052011 ; contaminated water was presumed to have caused most cases , especially in rural areas ( 4 ) .
holarctica has been isolated from drinking water sources in places where tularemia outbreaks occurred ( 7 ) .
the bacteria presumably came from dead animals ; a single infected water animal ( e.g. , vole , lemming , or mouse ) can contaminate up to 500,000 l of water ( 1 ) , and f. tularensis can survive in untreated water for months ( 2 ) .
free available chlorine residual concentrations routinely maintained in tap water systems can reduce f. tularensis by 4 log10 in 2 hours ( 8) . however , the malfunction of the chlorination device at sancaktepe village s main water storage tank enabled survival of the bacteria .
francisella species are fastidious and slow - growing and can be easily overwhelmed by competing organisms in environmental samples during culture ( 9 ) .
early september ; by that time , the bacteria might have been cleared from the water .
we spotted rodent activities , but no dead animals , near the implicated water source .
the imperfect case definitions and potential subclinical infections in asymptomatic villagers might have led to misclassification , which tends to bias the association toward null ; in other words , the observed association would have been stronger had there been no such bias , as evidenced by the sensitivity analysis that used laboratory - confirmed cases only .
this tularemia outbreak in northeastern turkey was associated with drinking contaminated tap water . at our recommendation
, the village administrator cut off the surface water source , repaired the chlorination device , and started checking chlorine levels regularly .
age distribution and clinical and signs and symptoms of probable and confirmed case - patients and findings of environmental investigations during a tularemia outbreak , sancaktepe village , turkey , july  august 2013 .
in 2013 , an oropharyngeal tularemia outbreak in turkey affected 55 persons . 
 drinking tap water during the likely exposure period was significantly associated with illness ( attack rate 27% vs. 11% among non  tap water drinkers ) . 
 findings showed the tap water source had been contaminated by surface water , and the chlorination device malfunctioned .