Published Date: 2012-06-01 16:52:37
Subject: PRO/AH/EDR> Psittacosis - UK (02): (Scotland), poss. person-to-person spread
Archive Number: 20120601.1153095
PSITTACOSIS - UK (02): (SCOTLAND), POSSIBLE PERSON-TO-PERSON SPREAD
A ProMED-mail post
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International Society for Infectious Diseases
Date: Thu 31 May 2012
Source: Eurosurveillance Edition 2012, 17(22) [edited]
Psittacosis outbreak in Tayside, Scotland, December 2011 to February 2012
[Authors: McGuigan CC, McIntyre PG, Templeton K]
Psittacosis is a systemic infectious disease caused by _Chlamydophila psittaci_. Usual features include fever, malaise, unproductive cough, headache, and atypical pneumonia. The incubation period is one to 4 weeks . Since its 1st description in 1879 , epidemics occurred during the next century. Where identified, the source of such outbreaks and infections was zoonotic, and predominantly avian but not necessarily psittacine. For example, large outbreaks occurred among poultry workers . Subsequently, these have become rare, as avicultural hygiene has intensified. In Scotland, up to 10 sporadic cases per year were notified (no outbreaks) in the past 10 years (Table [for tables see source URL above] . We have found no case described in the literature where person-to-person spread has accounted for cases of psittacosis, although person-to-person transmission has evidently been suggested but not proven .
Outbreak investigation and results
During a series of outbreak management team (OMT) meetings, results were assessed and further investigation directed. Awareness raising among Tayside medical practitioners aimed to increase case ascertainment. The investigation progressed on 3 fronts: epidemiological, microbiological, and environmental.
A modified Centers for Disease Control and Prevention (CDC) case definition  was agreed. To be considered, cases must have compatible clinical illness. All notified cases were interviewed about their illness, contacts, and relevant possible exposures. Confirmed cases had either _Chlamydophila_ species detected in respiratory secretions (by culture or PCR) or a 4-fold or greater increase in antibody (IgG or IgM) to _Chlamydophila_ species (to a reciprocal titre of 32 between paired acute- and convalescent-phase serum specimens taken at least 2 weeks apart) by CFT [complement fixation test]. Cases which were epidemiologically linked to a confirmed case were considered probable, given an antibody (IgG or IgM) titre of 256 or greater, and possible given one of 32 to 128 (all by CFT in a serum specimen taken after symptom onset).
Applying this, by 22 Feb 2012, the outbreak involved 3 confirmed, 1 probable, and 2 possible cases, with the index case having had onset of illness in late December 2011. The figure describes the time of onset and clinical course for confirmed and probable cases. These comprised 3 female and 1 male with an age range of 41 to 65 years. A further 2 possible cases were identified: a family member with mild respiratory illness and an unrelated patient from the same ICU as the index case.
Initial investigations used CFT performed according to standard methods using antigen obtained from Launch Diagnostics, Longfield, Kent, United Kingdom (UK) . The CFT antigen is a chlamydia group specific antigen. The test detects total complement fixing antibody: both IgG and IgM.
Real-time PCR was performed using in house assay on respiratory samples which were initially used for investigations for respiratory viruses. The screen for _Chlamydophila_ species was an assay targeted to 16S ribosomal sequences. Any positive sample was further investigated by specific real-time PCR to _C. psittaci_ or _C. pneumoniae_ targeting a different region of the 16S ribosomal sequence. This enabled determination of which _Chlamydophila_ species was involved in a case.
Of the confirmed cases, 2 showed a rising CFT titre, 1 a static raised titre. All were PCR positive. Sequence analysis of the outer membrane protein A (ompA) gene showed 100 percent similarity between these _C. psittaci_ strains. The probable case had a static CFT titre above 256 and was PCR negative. Possible cases had static titres of 64 to 128 and were PCR negative.
Extensive cartographical and field searches were made for possible avian sources of infection. These were directed by information gleaned from interviews with cases. Workplaces and residences of cases were plotted on an Ordnance Survey map. Cases 2 and 3 lived together 2 km [1.3 mi] from case 1. Case 4 resided a further 10 km [6.2 mi] west. Although not within any of the cases' respective place of residence, 2 pigeon coops and a cage of small birds were found in the neighbourhood of where cases 1, 2, and 3 lived. None were within 500 m [0.3 mi] of case 1, but as these could be considered a plausible source, faecal samples were taken for PCR analysis.
The index case's pet dog was reported to have rolled in the remains of a dead bird in December 2011. Also, this case's workplace was reported to be affected by a large number of gulls. Searches in both areas revealed insufficient sample material. On veterinary recommendation (included in the OMT), a PCR analysis of a pooled canine faecal sample was done, using an unpublished method, developed at the UK Animal Health and Veterinary Laboratories Agency, Weybridge. This PCR detects the presence of _C. psittaci_ and _C. abortus_ and was negative.
No environmental source of any _Chlamydophila_ species was revealed by environmental investigations. This is not unusual .
Since the source of the infection was thought to be a pathogen which was not readily transmissible from person-to-person, standard infection control measures were recommended for those HCWs [healthcare workers] and other people in contact with cases.
Discussion and conclusion
The main issue in this outbreak is the picture of person-to-person spread. The authors can find no description of this in psittacosis. Incubation ranging from 1 to 4 weeks implies up to 21 days between shortest and longest. The longest gap between onset of confirmed cases was 25 days. While the cases amongst the extended family might be explained by a putative persistent source to which family members were sequentially exposed (such as a geographical, not temporal, point source), case 4 (the HCW) cannot.
Since cases 1 to 3 were members of an extended family and had extensive and frequent contact with each other (especially over the winter holiday season) it was not possible to retrospectively identify particularly significant 'mutual exposure events'. However, shared exposures between case 4 and the others were sought. The only spatial-temporal overlap was with case 1 and occurred during the admission of case 1 to the ward where case 4 worked. Case 4's duties included personal care (not invasive procedures). Conceivably, case 4 may have been exposed while caring for case 1 who required intensive medical support and investigation. Since it was not possible to explore direct contact between the 2 cases, it is uncertain what such exposure might be.
It is difficult to explain all cases in this outbreak by exposure to a common non-human source. While inconclusive, features consistent with person-to-person spread are demonstrated. In our view, clinicians and public health specialists should therefore keep an open mind to the possibility of person-to-person spread of psittacosis despite the received opinion that this generally does not occur.
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[ProMED-mail has posted previously regarding this outbreak, now confirmed to be psittacosis. The possibility of human-to-human spread is suggested here. In the past, others have also suggested the possibility of this spread but, like here, it has not been truly proven. The epidemiology in this report is stronger to support person-to-person transmission than in the past. - Mod.LL
A HealthMap/ProMED-mail map can be accessed at: http://healthmap.org/r/2uyp.]