healthcare is provided by public and private hospitals , and there are 5 major burns units . in january 2005 , pustular lesions were observed on the foot of a patient in 1 of the burns units , and similar lesions subsequently appeared on other patients .
local health authorities were informed of the outbreak , and an investigatory team confirmed reports of similar infections in the city s other burns units , with retrospective identification of at least 19 probable cases occurring over a 5-month period .
most patients had a fever ( 39.0c40.5c ) for 23 days , followed by the appearance of an eruption(s ) .
lesions were typically small , rounded , umbilicated , and nodular in appearance with an erythematous base ( figure 1a ) .
they contained cheesy pustular material and increased in size ( from 12 mm to > 1 cm in diameter ) and severity over 78 days .
the lesions involved burn wounds and intact skin surrounding them , with the unhealed margins of the wounds being covered by a layer of thick yellow secretion .
some patients had a sparse rash ; others had closely spaced lesions that produced a cobblestone appearance .
a single lesion developed on a paramedical staff member s finger , and lesions developed around 1 patient s insertion site for an intravenous line ( figure 1b ) .
in all instances , the disease was self limiting , and patients recovered in 34 weeks .
c ) orthopoxvirus particles detected by electron microscopy ( em ) examination of negatively stained grids prepared from pustular material ( magnification 73,000 ) .
d ) transmission em examination of ultrathin sections of infected vero cell cultures showing classic intracytoplasmic orthopoxvirus factories and maturing virus particles ( magnification 21,000 ) .
results of bacteriologic and mycologic examination of biopsy samples , impression smears , and swab samples from lesions were negative .
histopathologic examination showed extensive ulceration and granulation , with epidermal necrosis and subepidermal edema plus acute and chronic inflammatory cell infiltration .
impression smears and biopsy tissues were sent to the special pathogens unit , national institute for communicable diseases ( nicd ) , sandringham , south africa , and to the health protection agency ( hpa ) , centre for emergency preparedness and response , porton down , salisbury , united kingdom .
electron microscopy of negative - stained grids prepared at hpa and ncid laboratories from pustular material showed orthopoxvirus particles , and examination of ultrathin sections prepared from infected vero cell cultures at hpa found classic orthopox intracytoplasmic virus factories and particle maturation sites ( figure 1c , d ) .
pcr was performed on nucleic acid extracted from the samples , using primers specific for regions of the orthopoxvirus hemagglutinin gene ( at nicd ) and b5r membrane protein gene ( at hpa ) .
after nucleotide sequences were determined for the pcr products , phylogenetic analyses were conducted in relation to corresponding orthopoxvirus sequences obtained from genbank , using methods described elsewhere ( 14,15 ) .
the causative agent was found to cluster with buffalopoxvirus isolates within the vaccinia subgroup of orthopoxviruses ( figure 2 ) , and 3 patients from 2 separate burns units were shown to be infected with the identical virus , which was distinct from other known buffalopoxvirus isolates . to investigate the possibility of a shared source of infection , 17 samples of saline , antimicrobial drug ointments , petroleum jelly , cotton dressings , and swabs in common use were obtained from the 5 burns units and tested by pcr at nicd ; no results were positive .
inquiries led to the suggestion that the outbreak was probably propagated by transfer of infected patients between burns units .
this hypothesis was confirmed when a policy to isolate all new admissions , including referrals from other burn centers , for their first 2 weeks in a unit successfully controlled transmission of new endogenous cases .
maximum likelihood phylogenetic tree based on a 955-nt alignment of the karachi isolate and 33 orthopoxvirus sequences of the b5r gene from genbank constructed with clustalw ( www.ebi.ac.uk/clustalw/index.html ) and tree - puzzle ( http://bioweb.pasteur.fr/seqanal/interfaces/puzzle.html ) ; figures at nodes represent puzzle support values . the orthopoxvirus types are indicated to the right .
control measures included education of staff , single - room or cohort isolation of patients infected or suspected of being infected with buffalopoxvirus , and reinforcement of infection - control practices , such as hand disinfection after contact with any patient . to reduce virus load in the environment ,
the measures proved effective in reducing transmission within burns units , but they did not prevent the sporadic arrival of newly infected patients .
buffalopoxvirus outbreaks reported to date have been geographically restricted , and human cases have been limited to persons with direct exposure to infected animals , usually in rural communities ( 111 ) .
this reported outbreak uniquely involved nosocomial infections in 5 widely separated burns units in karachi , pakistan .
however , buffaloes are the most common dairy animal in pakistan , even within the city limits of karachi , and buffalo fat , particularly in the form of butter or ghee , sometimes is used at home as a dressing for burns . thus , burn patients newly infected with buffalopoxvirus
due to disparity in the sophistication and cost of the care provided at the burns units in karachi , patients are often transferred or move themselves between units , thus facilitating the possible spread of infection . in this outbreak , 6 of the 19 patients with putative cases of buffalopoxvirus infection are known to have transferred between burns units during treatment .
the infection was of low virulence for humans . delay in recognizing and investigating the outbreak is cause for concern and can be ascribed to poor awareness and lack of resources .
 during 5 months in 20042005 , buffalopoxvirus infection , confirmed by virus isolation and limited nucleic acid sequencing , spread between 5 burns units in karachi , pakistan . 
 the outbreak was related to movement of patients between units . 
 control measures reduced transmission , but sporadic cases continued due to the admission of new patients with community - acquired infections . 