Outbreaks to Pandemics 👣
An outbreak is defined as more cases of a disease than expected in a specific location over a specific time period.
Types of outbreaks:
-
Point source outbreaks:
Common source outbreaks where the source has infected cases at one particular geographical location, during a short period of time, are called 'point source outbreaks'. In such situations the source is said to be located 'at a single point in time and place'.
2. Continuing common source outbreaks:
When all (or most) cases in an outbreak have been infected by the same source, however over a prolonged period of time, then this type of outbreak is called 'continuing common source outbreak'.
3. Propagated outbreaks:
When an infectious disease is communicable (i.e. can be transmitted from person to person), then we can no longer consider that a single, common source is responsible for the outbreak. The causative agent is propagated within the population through human contact patterns.
​
2009 H1N1 INFLUENZA PANDEMIC
​
2009 H1N1 was first detected in the United States in April 2009. This virus was a unique combination of influenza virus genes never previously identified in either animals or people. Initial reports referred to the virus as a swine flu origin influenza virus because the virus genes were a combination of genes most closely related to North American swine lineage H1N1 and Eurasian lineage swine origin H1N1 influenza viruses. Investigation into the initial human cases did not identify exposures to pigs and it became apparent that this new virus was circulating amongst humans and not amongst pig herds.
​
EPIDEMIOLOGY:
​
The agent: Gene sequencing shows a new subtype of influenza A(H1N1) virus with segments from four influenza viruses: North american swine, north american avian, human influenza and eurasian swine
Host factors: The majority of these cases have occurred in otherwise healthy young adults.​​
Transmission: The transmission is by droplet infection and fomites.
Incubation period: 1-7 days
Communicability: From 1 day before to 7 days after the onset of symptoms. If illness persists for more than 7 days, chances of communicability may persist till resolution of illness. Children may spread the virus for a longer period.
​
CASE DEFINITION FOR 2009 H1N1 INFLUENZA PANDEMIC
​
Suspected case of Pandemic influenza A (H1N1) virus infection:
A person with acute febrile respiratory illness (fever> 38C) with onset:
-
Within 7 days close contact with a person who is a confirmed case of pandemic influenza A (H1N1) virus infection, or
-
Within 7 days of travel to community where there are one or more confirmed pandemic influenza A (H1N1) cases, or
-
Resides in a community where there are one or more confirmed pandemic influenza cases
​
Probable case of pandemic influenza A (H1N1) virus infection:
A person with an acute febrile respiratory illness who:
-
Is positive for influenza A but unsubtypeable for H1 and H3 by influenza RT-PCR or reagents used to detect seasonal influenza virus infection, or
-
Is positive for influenza A by an influenza rapid test for an influenza immunofluorescence assay plus meets criteria for a suspected case
-
Individual with a clinically compatible illness who died of an unexplained acute respiratory illness who is considered to be epidemiologically linked to a probable or confirmed case
​
A confirmed case of pandemic influenza A (H1N1) virus infection:
A person with an acute febrile respiratory illness with laboratory confirmed pandemic influenza A (H1N1) virus infection at WHO approved laboratories by one or more of the following tests:
-
Real time PCR
-
Viral culture
-
Four fold rise in pandemic influenza A (H1N1) virus specific neutralizing antibodies
​
TIMELINE OF THE PANDEMIC
17 April,2009 | Second human infection with the new influenza A H1N1 virus detected in California about 130 miles away from first infection, with no known connection to the previous patient |
18 April,2009 | First novel 2009 H1N1 flu infections were reported by CDC to the World Health Organisation (WHO) through the U.S. International Health Regulations Program |
21 Aril,2009 | CDC publicly reported to the first two U.S infections with the new H1N1 virus. CDC began working to develop a candidate vaccine virus |
22 April,2009 | CDC activated its Emergency Opreations Centre (EOC) |
23 April,2009 | Two additional human infections with 2009 H1N1 were detected in Texas, transforming the investigation into a multistate outbreak and response |
24 April,2009 | CDC uuploaded complete gene sequences of the new H1N1 2009 virus to a publically acessible international influenza database |
25 April,2009 | The WHO declared a public health emergency of international concern |
26 April,2009 | The United States Government declared 2009 H1N1 a Public Health Emergency of International Concern and CDC began releasing 25% of antiviral drugs needed to treat this new influenza virus from the federal stockpile |
27 April,2009 | WHO Director-General raised the level of influenza pandemic alert from phase 3 to phase 4, based on data showing person-to-person spread and the ability of the virus to cause community-level outbreaks |
29 April,2009 | WHO raised the alert from phase 4 to phase 5, signalling that a pandemic was imminent and requested all countries to immediately activate their pandemic preparedness plans and be on high alert for unusual outbreaks of influenza-like illness and severe pneumonia |
01 May,2009 | l shipments of new CDC tests to detect 2009 H1N1 began |
06 May,2009 | CDC distributed updated recommendations for the use of influenza antiviral medicines to provide guidance for clinicians in prescribing antiviral medicines for treatment and prevention (chemoprophylaxis) of 2009 H1N1 influenza |
11 June,2009 | The WHO declared a pandemic and raisd the worldwide pandemic alert leevel to phase 6, which means the virus was spreadingto other parts of the world |
25 June,2009 | CDC estimated atkeast 1 million cases of 2009 H1N1 influenza had occured in the United States |
Early July | Reported cases of 2009 H1N1 nearly doubled since mid-June 2009. Three 2009 H1N1 influenza viruses that were resistant to the antiviral drug, oseltamivir, were detected in three countries |
22 July,2009 | Clinical trials testing the 2009 H1N1 flu vaccine began |
August | Additional oseltamivir-resistant 2009 H1N1 viruses were detected by CDC |
20 August,2009 | Second wave of 2009 H1N1 influenza activity began in the U.S |
01 September,2009 | More than 1000 test kits have been shipped to 120 domestic and 250 international labratories in 140 countries since May 1, 2009 |
15 September,2009 | The FDA announced its approval of four 2009 H1N1 influenza vaccines |
30 September,2009 | U.S states placed first orders of 2009 H1N1 vaccine |
05 October,2009 | First doses of H1N1 vaccine were given in the U.S |
16 November,2009 | FDA announced its approval of a fifth 2009 H1N1 vaccine |
December | Results of trials conducted among adults were published in December, and the data indicated that the immune response among vaccinated adults was excellent |
18 December,2009 | First 100 million doses of 2009 H1N1 vaccine were available for ordering |
January,2010 | Activity declined to levels below baseline, but persisted for several more months at lower levels |
11 August,2010 | WHO aanounced the end of the 2009 H1N1 influenza pandemic |