20 March 2003

Dear Doctor,

Since March 2003, an outbreak of atypical pneumonia has occurred in some hospitals in Hong Kong. As of 3 p.m., March 19, there were a total of 145 cases of atypical pneumonia, including five deaths. All atypical pneumonia case patients have radiological evidence of pneumonic changes. The salient clinical and epidemiological findings are shown in the following paragraphs.

The Prince of Wales Hospital (PWH) has the majority of cases, and they mainly concentrated in one medical ward (8A). A detailed analysis of 31 atypical pneumonia cases among health care workers (HCW) at PWH has been performed. Fifteen (48%) of the cases were female. The age range was 21 - 54 years (median 32 years). Clinical presentation of the case patients included fever (100%), malaise (100%), chills (97%), headache (84%), myalgia (81%), dizziness (61%), rigors (55%), cough (39%), sore throat (23%) and runny nose (23%). Patients often first presented with severe headache, dizziness and myalgia. Onset of fever was abrupt, typically with chills and rigors, and temperature persisted above baseline. In some cases, they experienced rapid deterioration with low oxygen saturation and acute respiratory distress requiring support with ventilator.

Initially the blood picture was normal. However, by day 3 - 4 of the illness, lymphopenia was commonly observed (>50%), and less commonly, there might be thrombocytopenia. Elevated alanine aminotransferase and abnormal APTT were sometimes seen while prothrombin time was usually normal. Creatine phosphokinase was raised in some cases.

In typical severe cases, chest x-ray began with a small unilateral patchy shadow, and progressed over 24 - 48 hours to become bilateral, generalized, interstitial/confluent infiltrates. Patchy chest x-ray changes were sometimes noted in the absence of chest symptoms. Acute respiratory distress syndrome might be observed in the end stage. Post-mortem lung tissue showed generalized alveolar damage and lymphocytosis without obvious viral inclusion bodies.

Cases have been treated with a variety of antibiotics and antivirals, including ceftriaxone, ciprofloxacin, oseltamivir and others. None has been proven to yield consistent results. High dose corticosteroids with or without ribavirin shows favorable response in some patients.

Based on the history of a few indicative cases, the mean incubation period is estimated to be 3 - 4 days, and the range can be 2 - 7 days.

The available evidence suggests the mode of transmission is most consistent with droplet spread through respiratory secretions. Since the introduction of heightened infection control measures and barrier nursing on March 10, the number of cases dropped substantially.

Epidemiological investigations revealed that seven atypical pneumonia cases, including the index patient of the PWH outbreak, were linked to a hotel in Kowloon. The index patient of the PWH outbreak, who had onset of illness on Feb 24, had gone to the hotel to visit a friend staying there during Feb 15 - 23. The other six cases lodged at the 9th floor of the hotel sometime between Feb 12 and Mar 2. One of these six had onset of illness before he arrived in Hong Kong and lodged at the hotel on Feb 21; and we believe that he was the source of infection.

Staff of this hotel had not reported sickness related to this outbreak, and they have been kept under medical surveillance. We believe there is no residual risk for customers and staff of the hotel as well as residents in the area. The 9th floor of the hotel has been closed for thorough cleansing and disinfection as a precautionary measure.

The Department of Health, the hospital laboratories, the Chinese University of Hong Kong (CUHK) and the University of Hong Kong have been performing extensive laboratory investigations. The CUHK has recently detected a virus belonging to the Paramyxoviridae family among the specimens. There have been similar reports from overseas. The World Health Organization will coordinate efforts to verify and confirm the findings, and more research will be necessary to understand the unusual behaviour of the virus.

The Government has been providing daily updates on this outbreak to keep the public informed of the latest situation. The Department of Health has launched a dedicated website on atypical pneumonia to provide health advice on the prevention of respiratory tract infection and the latest information on the cases. You are welcome to visit our website at http://www.info.gov.hk/dh/ap.htm For prevention of respiratory tract infection, please advise your clients to adopt the following measures:

• Build up good body immunity by having a proper diet, regular exercise and adequate rest, reducing stress and avoiding smoking;

• Maintain good personal hygiene, and wash hands after sneezing, coughing or cleaning the nose;

• Maintain good ventilation;

• Avoid visiting crowded places with poor ventilation;

• Put on a mask if taking care of a patient with respiratory symptoms and wash hands thoroughly afterwards;

• Put on a mask if suffering from respiratory tract infection to reduce the chance of spreading the infection to people around them; and

• When visiting hospitalized patients, take due precautions in infection control, e.g. wearing mask and gowns and wash hands thoroughly afterwards.