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Ebola Outbreak Receding in Liberia, Still Strong in Sierra Leone

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Back in late September, the press had a field day with a mathematical model developed by CDC that estimated that if left unchecked, the Ebola outbreak in West Africa could wind up infecting over 1.4 million people. Almost missed in the hysteria over that high number was the fact that this same model predicted that even with key public health measures (patient isolation, monitoring of at-risk population who had contact with infected people and safe burial practices) falling short of 100% implementation, the outbreak could be brought under control around January of next year.

Word has been leaking out for a while now that the rate of new Ebola infections in Liberia is falling. Reports in the Washington Post on October 29 and November 3 told us as much. A chart in the WHO Situation Report for November 5 drives home just how dramatic the decline in new cases has become:

WHO Ebola Situation Report November 5, 2014

WHO Ebola Situation Report November 5, 2014

As can be seen in the chart, the rate of new infections for the two most recent weeks is less than one fourth the rate at the peak of the outbreak. Unfortunately, the news for Sierra Leone is not as good. While the rate of new infections may be leveling off, it is not yet falling appreciably:

WHO Ebola Situation Report November 5, 2014

WHO Ebola Situation Report November 5, 2014

Digging into the WHO report a bit further, we can find some evidence for how this dramatic drop in new cases has been brought about. We see that 52% of cases are now isolated. The WHO target for December 1 has been set at 70%, with a target of 100% by January 1. When it comes to management of dead bodies, though, the December 1 target has already been surpassed. WHO reports that 87% of the dead are being “managed in a safe and dignified manner” while the targets were set at 70% for December 1 and 100% for January 1. Also, although no benchmarks are reported, WHO states that 95% of registered contacts were reached daily (although in the text of the report, there are suggestions this number may be somewhat overstated).

It should come as no surprise that progress in implementing these basic measures has had a huge impact on bringing down the rate of new infections. It fits perfectly with the CDC mathematical model and it also addresses the known biology of Ebola infections. Patients are most infectious at or near death, so establishing safe burial practices is vitally important. Conversely, identifying infected individuals through daily monitoring of the at-risk population and then isolating infected individuals once symptoms begin means that far fewer people are exposed to people producing large amounts of virus.

Sadly, those who remain exposed are the health care workers who are providing care to those who are infected. Despite shortages of equipment and supplies, WHO and other organizations are doing their best to overcome those shortages and to beef up training to reduce risk to these brave people on the front lines in the work to control the virus. As of this November 5 report, 546 health care workers have been infected, with 310 of them dying. Only four new infections were reported for the week ending November 2, so it is hoped that this rate is also dropping.

Had the alarmists who insisted that this was a new super-strain of Ebola capable of airborne transmission (or even a strain developed in a bioweapons laboratory), it is doubtful that these basic public health measures would have had such a dramatic impact on the rate of new infections. Perhaps those folks can go back to railing about chemtrails or the evils of vaccines, because basic boring science appears to be on the road to controlling the current outbreak before all of mankind succumbs.

In the meantime, we are at about two weeks into the three week incubation period both for anyone “exposed” by Craig Spencer or for Kaci Hickox (or anyone she “exposed”) to show symptoms. No reports of transmission so far, and the odds of any cases showing up are dropping very rapidly from the already very low levels where they started.

Ebola Transmission: Health Care Worker Practice Most Important Consideration

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Not long after we learned that a health care worker treating Thomas Duncan has tested positive for Ebola, I ran across this terse tweet from Mackey Dunn, the pen name of Don Weiss, who is “a medical epidemiologist with the New York City Department of Health and Mental Hygiene”. The tweet linked to this short but incredibly important blog post. In the post, Weiss notes the baffling development that a health care worker, who wore full personal protective equipment (PPE), contracted Ebola from Duncan even though at this point, none of his family or other close contacts, who did not have full PPE, have developed symptoms of the disease.

That set of facts prompts Weiss to pose the question “So, what does this tell us about Ebola and how we can attain control?” His answer begins:

One, that Ebola patients become more infectious as the illness progresses. The newly reported case in a healthcare worker had onset on October 10th. If we take 9 days as the mean incubation period for Ebola this means the healthcare worker’s exposure was sometime around October 1, which was day 8 of Mr. Duncan’s illness. This is similar to what was seen with SARS, that patients become more infectious (and dangerous) with time.

In setting up the circumstances for his question, Weiss had noted that Duncan was hospitalized, ending exposure to family members, on day 5 of his disease.

Although he doesn’t mention it, this aspect of Ebola, where patients produce more virus and become more infectious during the course of a fatal infection, also accounts for why burial practices are so important to containing the spread of Ebola. Patients produce the most virus and are thus at their most infectious at death.

The converse also appears to be true. Duncan was symptom-free when he flew from Liberia to Dallas on September 19 to 20. At 24 days since the end of that trip, we have now passed the incubation period, commonly given as 2-21 days, for Ebola to develop in anyone who could have been exposed during the flights. No infections among those airline passengers have been reported. I have yet to see a major media outlet mention this point, though.

We are now at 16 days since Duncan was hospitalized, ending his family’s direct exposure, so we have passed the two-thirds point of the incubation period for them (and well past the 9 days that Weiss gives as the average incubation period for Ebola).

The second part of Weiss’ musings on the infection of the nurse is extremely important:

Second, that only hospitals that are well prepared to care for highly infectious patients should be allowed to do so. Standard practice is to have a staff person dedicated to observing the donning (putting on) and doffing (taking off) of PPE. This observation should continue throughout the period of clinical care (from an ante-room with a window). Perhaps gentle reminders during the doffing can avoid the presumed situation in Spain where the nurse may have touched her face with a gloved hand.

When a patient presents to a hospital early in the illness there is time to transfer to such a facility. That’s the plan here in NYC. Bellevue hospital has a specially equipped ward to care for Ebola patients. Their staff are well trained. The number of healthcare workers entering the room should be kept to a minimum, especially after day 7 of the illness.

Weiss was prescient in his push for an observer for workers putting on and taking off PPE. In today’s New York Times, we have this on the CDC’s thoughts regarding improving practices for health care workers treating Ebola patients: Read more →