Hong Kong CDW: A Review of Psittacosis in 2018-2019

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Psittacosis - often called parrot fever - is a rarely reported, atypical bacterial pneumonia caused by Chlamydia psittaci. The CDC cites an average of 10 cases of Psittacosis reported each year in the US, although many others may go undiagnosed.

The CDC also reports:

Since 1988, there has been a decline in reported psittacosis cases. This decline may be the result of improved diagnostic tests that distinguish Chlamydia psittaci from more common Chlamydia pneumoniae infections.

As we've discussed previously, while community acquired pneumonia (CAP) is the #1 cause of hospitalization of adults with an infectious disease in the United States, in more than half of the cases the type of infection (viral, fungal, bacterial) is never actually identified.

A 2015 study published in the NEJM (see The CDC’s EPIC CA-Pneumonia Study) followed 2500 cases over 5 years and found that in the majority (62%) of cases no definitive pathogenic agent could be determined.

Luckily, even without a definitive diagnosis, patients can be treated empirically. Psittacosis generally responds well to Tetracycline, and most people treated are able to recover. Sadly, in 2017 we did see Japan Report 2 Fatal Cases of Parrot Fever (Psittacosis) In Pregnant Women, so not all outcomes are favorable.  

Hong Kong, with a population of roughly 7 million, reported psittacosis infections last year (n=17) at a per capita rate roughly 70 times greater than the United States, and has already reported 7 cases in the first 4 months of 2019. 

First some excerpts from today's Communicable Disease Watch, then I'll return with more. 

Review of psittacosis in 2018-2019

Reported by Dr Ashley FONG, Medical and Health Officer, Respiratory Disease Office, Surveillance and Epidemiology Branch, CHP.

In Hong Kong, psittacosis has been listed as a statutory notifiable infectious disease under the Prevention and Control of Disease Ordinance (Chapter 599) since July 14, 2008. The annual number of cases reported from 2013 to 2017 was stable at two to nine cases. An increase in the number of psittacosis cases has been observed since 2018. We reviewed the psittacosis situation in 2018 and 2019 in this article.

The Centre for Health Protection recorded 17 cases of psittacosis in 2018 and seven cases in the first four months so far in 2019(Figure 1). Among the 24 cases recorded in 2018 and 2019 (January to April), majority (23, 95.8%) were diagnosed by polymerase chain reaction (PCR). The cases involved 14 males and 10 females, with ages ranging from 35 to 86 years (median: 60 years). Eight patients (33.3%) had pre-existing medical condition(s).

The most commonclinical presentations included cough (95.8%), fever (91.7%) and shortness of breath (50.0%). All patients developed pneumonia and required hospitalisation, with five patients (20.8%) requiring admission to intensive care units (ICU) and one (4.2%) to high dependency unit. Two patients (8.3%) developed other complications (acute renal failure and deranged liver function respectively). patients recovered after treatment.

Twenty-one cases (87.5%) were classified as locally acquired infection, while the places of infection of the remaining three cases were undetermined as the patient had stayed both inside and outside Hong Kong during the incubation period but without obvious history of contact with birds in both places.

Regarding risk exposure, seven patients (29.2%) reported history of bird contact (visiting pet bird shop and/or keeping pet birds at home or contacting bird droppings) during the incubation period. The remaining 17 patients (70.8%) could not recall any known exposure to birds prior to their disease onset.

Twenty-two (91.7%) were sporadic cases without epidemiological linkage, while the remaining two cases were involved in a household cluster affecting a couple with common exposure to a parrot.

(SNIP)

In summary, there was an increase in the number of psittacosis cases in Hong Kong since 2018. The overall epidemiological characteristics and clinical characteristics of the cases recorded in 2018 and 2019 were similar to those in the previous few years (Table 1).

To prevent psittacosis, the public is advised to:

• Maintain good personal and environmental hygiene.
• Wash hands thoroughly after handling birds.
• Seek medical treatment if symptoms develop.

In the same issue, but not included in the above summary, Hong Kong's CHP reported two more cases already in May, bring 2019's total to 9 Cases.

Two sporadic cases of psittacosis
 
On May 10 and 16, 2019, CHP recorded two sporadic cases of psittacosis. The first case affected a 44-year-old female with good past health. She had presented with fever and myalgia since April 28, followed by cough and shortness of breath since May 2. She was admitted to a public hospital on May 4. The clinical diagnosis was pneumonia and she was treated with antibiotics. She remained stable and was discharged on May 12. Her sputum collected on May 5 was tested positive for Chlamydia psittaci DNA by polymerase chain reaction (PCR). During the incubation period, she had travelled to Shenzhen from March 30 to 31 and Zhuhai from April 19 to 21.

The second case affected a 61-year-old female with history of hypertension. She had presented with fever and cough since May 6 and was admitted to a public hospital on May 11. Her chest X-ray show d left upper lobe consolidation. The clinical diagnosis was pneumonia and she was treated with antibiotics. She remained stable and was discharged on May 16. Her sputum collected on May 12 was tested positive for Chlamydia psittaci DNA by PCR. She had no travel history during the incubation period.

Investigation did not identify epidemiological linkage between the two cases. Both cases reported no history of contact with birds or their excreta. Both of them did not keep any pets at home and their home contacts and travel collaterals were asymptomatic

Human infection, at least until recently, has been solely attributed to direct or indirect contact with infected birds. And birds are common pets in Hong Kong (see SCMP's Why a bird is the ideal pet for Hong Kong's small homes) and Southeast Asia. 


But in 2012, the journal Eurosurveillance carried a report called Psittacosis outbreak in Tayside, Scotland, December 2011 to February 2012, involving four family members and a health-care worker, which suggested human-to-human transmission.

The following year, in Sweden Reports Rare Outbreak Of Parrot Fever, we saw a credible report of human transmission of parrot fever, where a 75 year old man who died in Kronoberg appeared to have spread the infection to at least 8 close contacts, including healthcare personnel.

In 2014, the ECDC's Eurosurveillance Journal carried a follow up report called:

Eurosurveillance, Volume 19, Issue 42, 23 October 2014

Surveillance and outbreak reports

Multiple human-to-human transmission from a severe case of psittacosis, Sweden, January–February 2013

Proven transmission of Chlamydia psittaci between humans has been described on only one occasion previously. We describe an outbreak which occurred in Sweden in early 2013, where the epidemiological and serological investigation suggests that one patient, severely ill with psittacosis after exposure to wild bird droppings, transmitted the disease to ten others: Two family members, one hospital roommate and seven hospital caregivers. Three cases also provided respiratory samples that could be analysed by PCR. All the obtained C. psittaci sequences were indistinguishable and clustered within genotype A.

The finding has implications for the management of severely ill patients with atypical pneumonia, because these patients may be more contagious than was previously thought. In order to prevent nosocomial person-to-person transmission of C. psittaci, stricter hygiene measures may need to be applied.

And just over a year ago we saw another example, in PLoS Currents: A Psittacosis Outbreak Among Office Workers WIth Little Or No Bird Contact - UK.

While H-2-H transmission of C. psittaci now appears possible, contact with infected birds still remains the primary suspected route of transmission.

Prior to the development of antibiotics in the middle of last century, the mortality rate from psittacosis pneumonia was on the order of 15% to 20%.

A 2007 EID Journal report Chlamydophila psittaci Transmission from Pet Birds to Humans looked at the use (or over-use) of antibiotics at 39 breeding bird breeding facilities in Belgium, and found that more that 40% had used antibiotics to treat sick birds in the previous 12 months. More than 10% routinely gave antibiotics to birds prophylactically.

The authors warned:

Because of the risk of developing drug-resistant strains, as described for Chlamydia suis (12,13), regular use of antimicrobial drugs must be avoided.

With less than 30% of Hong Kong's recent psittacosis cases recalling recent contact with birds, exactly how and under what circumstances they became infected remains a bit of a mystery.

One worth keeping our eyes on in the months ahead.