One finds this transient epidemic merited only one appearance among the CICM papers. Its use in Question 19 from the first paper of 2013 follows the 2009 pandemic by four years. One may also find a similar delay in the appearance of SARS in Question 13 from the second paper of 2004. Using this logic, the savvy trainees were able to anticipate an Ebola question in the second paper of 2015 (Question 22). A MERS question cannot be far behind.
If one felt for whatever reason compelled to explore this pathogen in great depth, one may use this WHO (2009) clinical practice guideline statement as a starting point, and then move on to something like this article from Chest. It would be a mental exercise to satisfy one's curiosity, as H1N1 may never appear in the papers again; at least not until the next pandemic.
This is on the basis of a global pooled analysis of outcomes, available in 2011.
Overall, the risk factors were approximately the same as for the normal garden-variety seasonal influenza.
The WHO has also published a table of features which predict a more stormy course:
There are significant differences between the H1N1 cohort and the seasonal influenza patients:
SARS appeared in Question 13 from the second paper of 2004. MERS is too new, and has not yet made an appearance. LITFL has an excellent summary page dedicated to these coronaviruses, which contains precisely enough information to revise this exotic topic, but not too much so as to waste the precious time of the fellowship exam candidates. Published literature dealing with these pathogens is extensive and widely available; so as not to inundate the reader with references, this author will recommends only Chen et al (2006) for SARS, and Sharif-Yakan et al (2014) for MERS. These disease entities are lumped together with H1N1 in this revision chapter, owing to the following similaries:
Coronaviruses (and related toroviruses) are mainly respiratory pathogens. They are the largest known RNA viruses; the particle is a huge discoid lipid-enveloped positive-sensesingle-stranded RNA virus, with a code length of approximately 30 Kb. The group contains many animal-specific species, such as the porcine transmissible gastroenteritis virus, the porcine diarrhoea epidemic virus, the feline infectious peritonitis virus, the mouse hepatitis virus, and various others. Until SARS and MERS there were only two recognised human coronovirus species, which both caused a mild case of the snots and sniffles.
The WHO criteria which acted as a definition of SARS, and which were mentioned in the college answer to Question 13 from the second paper of 2004:
The CDC criteria adds radiographic findings in patients with respiratory illness without known aetiology. SARS has generally been a diagnosis of exclusion, because no satisfactory rapid bedside test was available through much of the epidemic.
SARS coronavirus has not been seen since 2003. Apparently, it had originated in the Chinese horseshoe bat, Rhinolophus sinicus. The civet cat acted as an intermediate host. The first cases occurred in occurred in November 2002 in Foshan, Guangdong Province in southern China. Vietnam, Hing Kong and Canada followed, and ultimately cases were reported from 29 different countries. The epidemic ended in July 2003 with a total of 8098 cases, of whom 774 died. For those interested, WHO maintain a summary record of probable cases. Transmission occurred by a combination of direct contact, small droplets and aerosols. It did not help that the index case in Hong Kong (an elderly Chinese physician) received a nebulised bronchodilator in the overcrowded and poorly ventilated hospital ward, infecting one hundred and thirty eight other patients and healthcare workers. The peak infective period, when viral load is at its highest, is also the period of the most aggressive symtoms, when the patient is most likely to be hospitalised. This makes heathcare workers the most vulnerable group in terms of viral transmission, The greatest risk was to the ICU staff, particularly those who worked closely with intubated and NIV-ventilated SARS patients.
Clinically, the incubation period lasted 2-10 days. The following signs and symptoms were noted among the earlier victims:
The patients did not report much sputum production, and were not complaining of sore throats or rhinorrhoea. Weirdly, children had a milder course of infection; only adults were hit with the full-scale ARDS. The case fatality rate for SARS was <1% for patients aged 24 years or younger, 6% for 25–44 years, 15% for 45–64 years, and >50% for patients aged 65 years or older.
Investigations typically revealed the following features:
Radiological features were boring ARDS-like peripheral pulmonary infiltrates. 20% of the patients fit the contemporary criteria for ARDS. The lungs were fragile; in spite of wide adoption of lung protective ventilation strategies 26% of the patients developed some sort of barotrauma.
Attempts at specific management consisted of ribavirin, ritonavir, lopinavir and pulsed methylprednisolone. Interferon and monoclonal antibodies were trialed. Of all these, nothing showed any sort of favourable effect on outcome. Steroids were even associated with an increased 30 day mortality.
The index case of MERS was tracked retrospectively to a hospital in the city of Al-Zarqa in Jordan, in April 2012. The CDC has a regularly updated page dealing with the evolving situation. Their clinical definition of a MERS case includes fever and pneumonia or ARDS, as well as epidemiological risk factors (eg. recent travel to a country with an outbreak, or recent contact with a symptomatic traveller). Confirmation of a case requires PCR identification.
Incubation period is around 2-14 days (median = 5). Again, bats are probably the native reservoir, and camels may be the intermediate host. Clinical signs and symptoms are very similar to SARS, and include the following:
Unlike SARS, sore throat and coryza are more common. There is usually also nausea and vomiting, dizziness, sputum production, diarrhea, vomiting, and abdominal pain.
Sharif-Yakan et al (2014) report 707 cases, from three continents. The current case fatality rate approaches 35%. Of the patients that end up requiring ICU admission, this mortality statistic approaches 60%, with a median ICU stay of around 30 days. Again, no effective therapy or prophylaxis for MERS-CoV exists. Fortunately, several Hajj seasons have now passed without a fearsome worldwide outbreak, which may mean that this virus may ultimately retreat into the realm of virological pub trivia.
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